When you roll damage for an attack you make with a melee weapon that you are wielding in two hands, you can roll one extra die of the weapon’s base damage dice and discard the lowest of the weapon’s base damage dice. The weapon must have the two-handed or versatile property for you to gain this benefit.
If you are 6th level or higher, you’ve also learned to put the weight of a weapon to your advantage, letting its momentum empower your strikes. You use your Strength and a half instead of Strength for the damage rolls of melee weapons that you are wielding in two hands.