Marvel vs Capcom 2/Basic Mechanics
Marvel has six buttons, but instead of leading from jab to fierce like many other 2d games, Marvel designates the last button of each row as an assist button. The first buttons of each row act as jab (then strong) and short (then forward) while the middle buttons act as fierce and roundhouse.
If jab or short is quickly pressed twice, it will result in a 2-hit combo of jab-strong or short-forward.
Each character has his or her own launcher, the attack that sends the opponent into the air so that you can perform an air combo. This button is primarily either a down-forward fierce or roundhouse; however, it is character specific and some characters in particular can launch without fierce or roundhouse (Magneto can launch you with standing strong).
Marvel also allows every character to perform a regular jump and a superjump.