How can i make a melee combat system where the clients can damage each other

Hi guys
I am a beginner ue4 user. Finally i made a dedicated server, my goal is to make a mmorpg project. The problem that i watched several tutorials to make a combat system but it is only works against AI. I know i should not start with a multiplayer project but the RPG style is not drives me. I just would like to make where i can make a pvp arena with my friends.
I hope someone can help me.