In the function changeWheel() we first want the timeline to go to the framename "repeat" in frame 2 to repeat plying the movieclip for the number of times (i) we define. Then we have several if statements where whenever the value of i changes, we create a new wheel and change the color of the tire of the new wheel. You can of course change whatever you want or just repeat the movieclip.
In frame 2 we increase the value of i by 1 writing i++;. Whenever the timeline goes to this frame ("repeat"), i is incremented by 1. In frame 10 we the function changeWheel() is called. And this is all there is to this little clip.