Controls can be changed in the Options menu. Be sure to save. If you get an error while saving, open the game with Run as Administrator.

While different characters have different controllers, the buttons are usually as follows:
A = Light Kick, B = Medium Kick, C = Heavy Kick

X = Light Punch, Y = Medium Punch, Z = Heavy Punch

The game supports Microsoft XBOX 360 Controllers, and is already set up to use them for up to two players. The default controls are as follows: