iRacing is a realistic computer racing simulation in which you race against other real people. There are no "computer cars" in iRacing, you race only against other people. If you crash or drive unpredictably, you will probably cause other people to hit your out-of-control car and crash, and they may be quite unhappy about it, and sometimes let you know in no uncertain terms.
iRacing is a subscription service. You must be online to race at iRacing, even to practice on a track by yourself with no other racers. Subscriptions are currently about $10 per month or $100 per year. In addition to the subscription cost, you will probably end up buying cars (about $12 each) and race tracks (about $15 each), which can add up to one or two hundred dollars to get everything you need to enter one season (12 weeks) of races in one series. Once you buy a car or track, you have it forever (cars and tracks are not a subscription, in that you do not have to pay again for a car or track to use it in another season or series).
You need a PC with a good graphics card in it, and a force-feedback wheel and pedals. A decent starter wheel and pedals from Thrustmaster or Logitech is about $300.
iRacing lets you race a variety of cars on many different tracks, and has a few dozen "official series" in which you can compete.
The cars you can race are listed at https://www.iracing.com/cars/. When you join iRacing, you get a set of "included" cars to start out (they are marked with a green "included" banner on the web page). Typically you'll begin your iRacing career in road races in the Mazda MX-5 Cup car or in oval races in the Street Stock car. (iRacing also has dirt track racing, both dirt ovals and dirt road courses, but I am not familiar with them.) Eventually you'll probably want to move beyond the starter cars, and you'll want to buy cars (all the way up to Formula 1 , Indy Car, NASCAR Cup, and different kinds of prototype or sports cars) to enter other kinds of races. You buy most cars for about $12 and you own a car forever once you buy it.
The tracks you can race are listed at https://www.iracing.com/tracks/. When you join iRacing, you get a set of "included" tracks to start out (they are marked with a green "included" banner on the web page). You'll probably begin your iRacing career in a Mazda MX-5 Cup road race series or the Street Stock oval series, and all of the tracks used in those series are included with your subscription. Eventually you'll probably want to move beyond the starter cars and starter series, and you'll want to buy tracks raced by other series you're interested in. You buy most tracks for about $15 and you own them forever once you buy them.
iRacing offers a few dozen "official series" that you can race in, though each series sets certain skill requirements so you won't be able to enter anything you want right from the beginning, you'll need to work your way up to more advanced series (just like real life racing). You don't really need to enter a full series, you simply enter any race in any series that you want to race and are eligible for. You can race a single race in a series or all of the races. Each series races one car, or sometimes a small collection of cars from which you can choose (again, similar to real life, where for example the 24 Hours of Le Mans races many different kinds of cars simultaneously).
Most series in iRacing follow a common schedule of seasons. A season is usually 12 weeks long, and races at a different track each week. The week changes at 00:00 GMT on Monday night / Tuesday morning (so, 7pm Monday Eastern Standard Time, or 8pm Monday Eastern Daylight Time). Each series publishes its schedule a week or two before the start of a season. A season schedule for a series will list for each of the 12 weeks of the season the track for that week's races, how many laps (or how long, for a timed race) the race will be, and the simulated time of the race (some races are at night, and at different times of the year -- for example in November 2020 many of the races are taking place in April of 2021, which mainly means that air and track temperatures, and the angle and movement of the sun during the race, match what they will be in real life in April of 2021).
Each series has standings for its season. You receive "championship points" for each race you enter, and the number of points depends on your finishing position in the race and the overall skill level of all of the racers in the field for that race. Your place in the standings is determined using your 8 highest-scoring weeks of the season. You can enter a race as many times as you want during a week, and your score for the week is the average of the top 25% of the scores from the races you entered.
Each racer in iRacing has 4 licenses, one for each of these different types of racing: Road Racing, Oval Racing, Dirt Road Racing, and Dirt Oval Racing. There are 4 main "classes" of license: A, B, C and D. D is the lowest-level license, and A is the highest. In addition to these main classes, there is a Rookie license class where everyone starts, and there are a couple of levels of Pro license classes (which I know almost nothing about). If you never enter a particular type of race (for example, I have never entered a dirt road race), your license for that kind of racing will stay at the Rookie level forever.
Your license class is the result of a Safety Rating you have for each type of racing (road, oval, dirt road, dirt oval). Your Safety Rating is based on how many "incident points" you have incurred and how many corners you have driven through over a very long period of time (it is not publicly known how long). The Safety Rating is basically a function of the ratio of incidents to corners driven. Your Safety Rating is a number between 0.00 and 4.99, and you begin your career as a Rookie with a Safety Rating of 2.50.
You incur "incident points", which are kind of like points against your license, for different mishaps you have on the track in official race sessions. For example, you incur 1 point for going off the track (even just a little bit), 2 points for losing control of your car (even if you don't hit anything), 2 points for hitting a wall, and 4 points for making contact with another car. Incident accounting is on a "no fault" basis, which means that if I drive my car right into yours and wreck you, and it is all my fault and there was nothing you could have done to avoid it, you will get 4 incident points for making contact with another car (mine) and I will get 4 incident points for making contact with another car (yours). People often complain about this, but the software cannot reasonably decide who is at fault in many cases, and over long periods of time and many races the no fault system has the right outcome, even though it can be frustrating if you get a run of bad luck for a bunch of races in a row.
Your Safety Rating is adjusted after each race, based on adding that race's incident points and the number of corners you drove through to the statistics used to calculate the Safety Rating. Any time you cross a whole number boundary (if you go from 2.87 to 3.02, you cross the whole number boundary at 3), an extra 0.4 adjustment is made to your rating. This seems capricious, but the purpose of it is to prevent your rating from fluctuating in a way that makes you bounce in and out of eligibility for promotion (or demotion). For example, if you have earn a rating of 3.02 so that you would be eligible for promotion to the next license class (see below), you might be discouraged from entering any more races for fear that someone will wreck you and your rating will drop below 3. By adding a 0.4 bump, when you cross from 2.87 to 3.02, your new rating will actually be 3.42, and you can continue racing without jeopardizing your license level. Similarly if you drop after a race from 3.02 to 2.87, your new rating will actually be 2.47, after the 0.4 downward bump.
The Safety Rating calculation is different for different license classes. In many races, if you get 8 incident points (which is a lot), your Safety Rating will still go up if you have a D license, but down if you have a B license.
To get promoted, you first have to race in a minimum number of races for your current license class. For example, if you currently have a Class C license, you must race in some number of races that Class D license holders are not eligible for to be eligible for promotion. (Currently the minimum is 4 races, and you can satisfy it by entering the same race 4 times within the week.) Once you satisfy the minimum participation requirement, you get promoted to the next license class between seasons if your Safety Rating is above 3.00 at the end of a season, or you get promoted immediately if your Safety Rating is above 4.00 at any time. Similarly you will be demoted at the end of a season if your Safety Rating is below 2.00, and you will be demoted immediately any time your Safety Rating falls below 1.00.
One special case of promotion is that you will be promoted from Rookie to a Class D license immediately if your Safety Rating rises above 3.00.
When you are promoted, your safety rating is lowered by 1.00. So if you start a race with a 3.87 Safety Rating and it goes up to 4.02 after the race, you'll get a 0.4 bump for crossing a whole number, leaving you at 4.42, then you'll be immediately promoted to the next license class, and your Safety Rating will be set to 3.42.
You have a skill rating, called an iRating, for each type of racing (road, oval, dirt road, dirt oval). Each time you enter a race, your skill rating is adjusted based on your finishing position in the race. Within each race session that you run, iRating adjustments are a "zero sum game", meaning that the sum of the iRatings of all drivers in the session will be the same after the race as before it. So if someone's iRating goes up, someone else's iRating must go down.
Everyone gets a default iRating when they first join the service, and in most cases they won't finish very well in their first races, so their iRating goes down while they "give" iRating to the drivers finishing ahead of them.
Your iRating is used to place you into a "split" race session (see the "Races and Sessions" section) in each race so that if there are many drivers registered for a race, you'll compete with drivers whose skill level (as measured by iRating) is similar to your own.
You drive your cars in iRacing in a "session", and there are different kinds of sessions, one of which is a "race". I'll describe the various types of sessions here, beginning with race sessions.
Races take place at times specified for each series. The times are specified in GMT, so some series that only race every 2 hours change from odd to even hours (or the other way) when your location makes a Daylight Saving Time change. Popular races, such as the ARCA series that I race in, run races every hour, and other series run less frequently, such as Indy Pro which races every two hours.
A race session works like this:
You must register for the session sometime in the 30 minutes before its scheduled time. If you register and then do not actually run the race, you are given a last place finish.
Practice: The first 3 minutes of most race sessions is a practice period. Three minutes is not really enough time to practice anything, and typically the first minute elapses while your computer establishes a connection to the race server and sets up the track environment for you, so you've only got about 2 minutes to practice. The real purpose of the practice time is to give you a chance to make sure all of your equipment (wheels, pedals, headphones, microphone) is working as expected, and to drive a short while on the track to see what the track conditions are (traction changes quite a bit depending on the weather and the amount of rubber built up on the track).
Qualifying: After the practice time ends, you typically have either 8 (for a road course) or 5 (for an oval) minutes to qualify for the race. In all of the series I run, you qualify on the track by yourself (there are no other cars on track). You begin in the pits, you get a warmup lap from the time you leave the pits until you reach the starting line, and then you get two "hot laps" to qualify. Your qualifying time is the better time of the two laps.
Gridding: Once either everyone has qualified, or the qualifying time elapses, you have 2 minutes to "grid" your car, by pressing a "Grid" button in the simulation. Your position on the grid is determined either by your qualifying time compared to all other qualifiers, or if you did not qualify (either you elected not to, or you crashed in qualifying and never completed a lap) you are assigned a grid position behind all qualifiers. If you do not grid your car, you may still run the race, but you start from the pits, and the race officials will hold you in the pits until after the race starts.
Race: After all cars are gridded, or the gridding time expires, the race begins. F1-style road races begin with a standing start, and oval races and Indy Car-style races begin with a pace lap (or on a very short oval track, two pace laps) behind a pace car. In a standing start race, you line up and hold still and the race begins with a green light. In a rolling start (behind a pace car) race, the pace car pulls off the track, and the pole sitter (the leader, the first car on the grid) can usually choose when to begin the race by deciding when to accelerate.
This process means that the real start of a race is a pretty predictable amount of time after its scheduled time. For a road race scheduled to start at 3pm, you know there will be a 3 minute practice, 8 minutes of qualifying, and 2 minutes of gridding time, so the race will start at 3:13pm. (But you must register for it before 3pm.)
Many drivers may enter a given race, more than can reasonably or safely run together on the track. Each series has some maximum number of drivers in a race session, and if the number of entries goes above that number, the race is divided into separate "splits", where each has some subset of the drivers who registered. You get assigned into a split based on your skill level (iRating), so that you are competing with drivers about like yourself. In the ARCA races I run, there are frequently more than 150 drivers registered for a race, and they get divided into splits so that there are 6 different race sessions with 25 drivers each. The splits are formed before the race session begins, and once you are placed into a split and a race session, you go through the whole session (practice, qualifying, gridding, and racing) with that same group of drivers. (This is why you must register before the scheduled session time, even though the race will start 10 or 13 minutes later.)
Practice sessions are like race sessions in that there are other drivers on the track, but you can join or leave a practice session any time (they are usually about 2 hours long, and there's usually always a practice session available for the current week's track in every series), and any incidents you have will not be counted against your Safety Rating. It is still a good idea to be courteous and predictable on the track, because you are driving with other racers that you will likely see at some point in a real race.
A test session is one where you are running on the track by yourself. You will still be notified about incidents (such as leaving the track or hitting a wall) and how many incident points they incur, but nothing in the session will be applied against your Safety Rating.
I rarely run this kind of session, but a time trial is a session where you are alone on the track, but incident points and laps (turns) count against your Safety Rating, though at a "discounted" rate. There is an "official" time trial competition in iRacing, where you try to achieve better lap times than other racers, and there are points and standings for time trial performances. But possibly the main use of time trials is that if you are in dire need of a Safety Rating improvement and you can't afford to take the chance that someone crashes you in a race, you can gain Safety Rating by running a lot of time trial laps. I did this once in my career, to get beyond my Rookie oval license, because the Rookie Street Stock series (the most common one for beginners) is loaded with drivers who can't hold their car on a racing line at all, and driving reasonably always gets you wrecked. Once I got to 2.92 (with many ups and downs as I kept getting wrecked by others) and needed to get to 3.00, I ran 90 laps somewhere in a time trial to get to 3 and get out of the Rookie class.