When you hit a creature with a weapon attack, you can expend one superiority die to attempt to knock the target down. You add the superiority die to the attack's damage roll, and if the target is Large or smaller, it must make a Strength saving throw. On a failed save, you knock the target prone.

What is the superiority dice?

Superiority dice allow you to hit an opponent for damage and do an extra effect. Otherwise you just can make the attempt to disarm, damage an object, or shove as an attack with no damage.

How do you increase superiority in dice?

You have four superiority dice, which are d8s. A superiority die is expended when you use it. You regain all of your expended superiority dice when you finish a short or long rest. You gain another superiority die at 7th level and one more at 15th level.