Pit stops allow you to change tyres. You can pick between Soft, Medium, Hard and Wet. You can also choose to Service your car, this will restore your Car Condition bar to 100% and also fix any component failures your car suffers during the race.
You can stop as many times as you like but it’s important to remember that you cannot refuel when you pit stop! You will need to manage your fuel so that it lasts for the whole race. Try not to pit stop both your drivers at the same time or one will have to wait and will lose time!