Source: Player's Handbook

You have mastered ranged weapons and can make shots that others find impossible. You gain the following benefits:

• Attacking at long range doesn't impose disadvantage on your ranged weapon attack rolls.

• Your ranged weapon attacks ignore half and three-quarters cover.

• Before you make an attack with a ranged weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If that attack hits, you add +10 to the attack's damage.