Making Host Game Function

Hi, i wanna play a game with unity but i really dont know how to build host game function for playing the game with friends. I want a basic system like this. 2 Players add each other to friendlist in game than one of them host room and send invite another for join room. Just i wanted to playing with friends not the whole world.. Can you discuss me any video tutorial about it or can anyone help me with that ?

And should i buy any server for this function works ?