While wielding a shield, you gain the following abilities:

When you are wielding a shield and not incapacitated, you can add your shield's AC bonus to any Dexterity saving throw you make against a spell or other harmful effect targeting you.
As a bonus action, you can also push a creature within 5 feet of you up to 5 feet away from you if it is one size larger than you or smaller.
When you are wielding a shield, you can use a reaction with that shield when hit by an attack to change armour class bonus for wielding a shield to be equal to your Strength modifier against the triggering attack, potentially turning the hit into a miss.