Question i'm new in multiplayer in unity and i want some help please

Hi, i never made a multiplayer game in unity so i am asking you guys to explain some things to me. I have basic knowledge of networking (I know the individual layers in the iso/osi model and what they do and what they are responsible for, etc.), but I don't know how to connect these dots. what is this photon or mirror responsible for and can they be combined with steam in some way if I would like to release the game on it. or you don't need these things at all and I can set up a server in my house, but again - how to connect it to the unity.
I just want someone to tell me how or by what software I can have multiplayer in unity (or I don't need any). please understand that i'm just getting started with this so i'd like someone to put me on the right track.

 

I would suggest you look up some beginner tutorials on youtube. Those will explain how to use photon, mirror, steam, anything you want to learn is on youtube. Make a basic game with both Mirror and PUN2 and see which one you like better, then stick with it. Games have been released using both so there isn't really a bad option.