When I do the DamageEvent and build it, there are many errors pop up and I not sure what should I do to fix those.
Unreal 5.4/5.5? You probably need an additional include to get the FPointDamageEvent type into your code. In 5.4 or later they changed the required includes for many things. Have a look here and try adding the include
FPointDamageEvent | Unreal Engine 5.5 Documentation | Epic Developer Community