From the last update of the game it is possible to customize your car!
To do this, enter the second icon in the lower options bar, where you will see different versions of the car to equip. As soon as you enter, you will see the "Classic" car which is the one that will be assigned to you by default.
As you get coins in your games and in the ranking you can buy cards that will unlock an available car; once you unlock it, you can equip it to use in your games. You will be able to see the cost of each card in the box “Buy card”. Below the card you want to get you will see its progress until reaching it; as you want to get better cards the cost of these will increase.
In turn, you will see cars that are momentarily unavailable until you move up the league in the rankings. (Inside the card you will see in which league you can get it).
At the top of your screen, you can see your coin balance.