You gain the following benefits.

Ability Score Increase. Increase your Strength or Dexterity score by 1, to a maximum of 20. You cannot benefit from this again if you already have Weapon Master Technique.

Critical Mastery. When you hit a creature with a weapon that you are proficient in with weapon mastery, you score Critical Hits on a roll of 18, 19, or 20.

Weapon Mastery. When you hit a creature with a weapon that you are proficient in with weapon mastery, as part of the Attack action on your turn, you can cause the weapon to deal extra damage to the target. The extra damage equals your half of your Proficiency Bonus, rounded down. If you have Weapon Master Technique this bonus is increased to your full Proficiency Bonus.

Fighting Weapon Style. When you roll damage for an attack you make with a Melee weapon that you are proficient in with weapon mastery, you can treat any 1 or 2 on a damage die as a 3.