depends on what settings you're using. This is default settings:
Left analog stick: move/strafe
Right analog stick: look around
Left analog stick click: sprint
Right analog stick click: knife
A: jump/climb over things
B: tap for crouch, hold for prone
Y: switch weapons
X: Reload, action/event button
Left Trigger: aim using sights
Right Trigger: fire weapon
Left bumper: special grenade
Right bumper: frag grenade.
D-pad: varies on your equipment.