You gain the following benefits.

Ability Score Increase: Increase your Strength score by 1, to a maximum of 20.

Shield Protection: When having a Shield equipped, adjacent allies have Half Cover.

Shield Wall: When 2 or more characters with this feat are adjacent to each other while having a Shield equipped, they all have Three-Quarters Cover.

Reactive Bash: When an enemy misses you with a melee attack  while you have a Shield equipped, you can use your Reaction to force the target to make a Strength saving throw (DC 8 plus your Strength modifier and Proficiency Bonus). On a failed save, you either push the target 5 feet from you or cause it to have the Prone

condition (your choice).