There are four types of Normal Attacks: a "Weak Attack", done with the A button; a "Medium Attack"", done with the B button; a "Strong Attack", done with the C button; and a "Drive" done with the D button. The Weak Attack does minimal damage, but is usually the fastest. Strong Attacks do a decent amount of damage, but is much slower than the Weak and Medium attacks. For most characters, attacks can be linked from weak to strong: A to B to C-to create a combo.
High, Low, and Mid Attacks
Mid attacks can be blocked while crouching or standing, High attacks can only be blocked while standing, and low attacks can only be blocked while crouching.
Inputting certain commands with the four types of Normal Attacks will cause your character to perform a special attack.
Every attack has a recovery animation, which leaves you unable to do anything. Revolver Action allows you to perform a Normal attack immediately, without waiting for the recovery animation to complete. For example, if your opponent blocks a standing B, you can immediately follow up with a standing C, without waiting for the recovery annimation from the standing B to complete. The act of skipping the delay at the end of an attack is referred to as a "Cancel". Some attacks can be canceled into each other, while others cannot.