Press the R1 or RT button or the R2 ot RB button to enter the attack mode and press the X button to attack with the equipped weapon. Use the directional button or left analog stick to aim. (Some weapons do not apply.)
When no weapon is equipped, the X button unleashes a tackle when pushed in attack mode. By pushing the directional button or left analog stick down or away while doing so, you can perform a kick.
Pressing the R1 or RT button will aim automatically at the nearest enemy. Pressing the R2 or RB button will aim in the direction you are facing. Press the L1 or LT button toggle between multiple targets when applicable.