set Angle is quite simple to understand.
When you have a sprite selected, you see handles to resize it, and also a center point, with a handle on its side, to rotate the sprite. Basic orientation is 0�.
If you set another angle on the sprite, it will rotate around its center, the origin point, witch you can change in the animation editing interface (dbl click on the sprite). Be carefull, there is a different center for each frame of each animations !
How to implement the mats in C2 ? Depends how your "car" is built. If it's, let's say, 1 sprite for the body of the car, and 1 sprite per wheel, you should put those in a container.
In the event sheet, I would create a function "car.move" (with a direction and a speed maybe ? Everything depends on your implementation). In this function, I would put some action on the car wheel sprite, "set angle to dt*car.speed*360/(3.1415*Sprite.width) + wheel.angle". Of course, you would have to change car.speed, Sprite.width and wheel.angle with the right variables, depending on the name of your objects and the behavior you use to move the car (how the speed is store)