To use this ability, you must first successfully parry an opponent's melee attack. If your opponent leaves an opening, you can use your reaction and expend one superiority die to make a counter-melee weapon attack with your main weapon.
Abilities are linked to certain classes and can be used by both players and non-player characters (NPCs). To use most abilities, you must first learn them and sometimes invest points into them. Occasionally, you may come across special ability scrolls with a limited number of uses. These scrolls allow you to use the ability even if you have not learned it, but you can only use the ability a certain number of times before the scroll is depleted.