MAME lists all buttons as button 1 button 2 etc, what they're actually mapped to can change from game to game. Look at the differences between Samurai Showdown, Street Fighter, and Guilty Gear. They have completely different controls, but if you were to look at them from a button view, like there are three buttons on top, three buttons below for Street Fighter, it gets a lot simpler when planning out your MAME controls.