If you take the Attack action on your turn, then you can use your bonus action to try and shove a creature within 5 feet of you with your shield (deals 1d4 piercing damage if you are using a spiked shield).

If you aren't incapacitated, you can add your shield's AC bonus to any Dexterity saving throw you make against a spell or other harmful effect that targets only you. If you are subjected to an effect that allows you to make a Dexterity saving throw to take only half damage and you are wielding a medium or larger shield, then you can use your reaction to take no damage if you succeed on the saving throw, interposing your shield between yourself and the source of the effect.