how to detroy an actor ( rocks ) with the characters fists ???

You just destroy the actor, with the DestroyActor node.

If the actors are static meshes, you’ll need to do some sort of trace ( line trace, sphere trace etc ) from the player, and destroy it that way.

If the actors are blueprints, you can send them a message using interfaces that they’ve been hit, and they destory themselves.

Blueprint interfaces: