You gain a +1 bonus to Defense

Additionally, if you are wielding a shield and you aren’t incapacitated, you can add your shield’s Defense bonus to any Reflex saving throw you make against a spell or other harmful effect and when you are subjected to an effect that allows you to make a Reflex saving throw to take only half damage, 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.

If you are 6th level or higher, when a creature within your reach makes an attack against a target other than you, you can use your reaction to make a melee weapon attack against the attacking creature.