This Unreal 5.3 Gameplay Ability System video is about applying Damage to our recently created Health Attribute by using a GE_Damage Gameplay Effect. We do this by first creating the Health Changed Delegate so that we can see Health Changes in the Editor. Next we build the GE_Damage Gameplay Effect and apply it to the Character, and then convert it to use SetByCaller instead.
https://dev.epicgames.com/community/learning/tutorials/aDvz/unreal-engine-06-damage-gameplay-effect-let-s-make-a-top-down-shooter