Overview

Having a fully functional multiplayer game?
Chances are, you want to release it on Steam. And you want to benefit from Steam's API, for example, by using its lobby system, instead of punching NAT holes.

Before continuing, I suggest reading/watching the below resources:

The Steamworks.NET API

https://steamworks.github.io/

Demo of Forge&Steamworks.NET Implementation

Clean and perfectly working!
Has fully functional lobby + friend + avatars
I highly suggest to read its code, if not use it outright to skip parts of this "tutorial"
https://github.com/phalasz/forgesteamworksexample

Installing Steamworks.NET

https://steamworks.github.io/installation/

Original/Raw installation, of Steamworks.NET

https://www.youtube.com/watch?v=o5-Y-5Dtg_c

Uploading to Steam&Managing Builds

https://www.youtube.com/watch?v=rK5Fr5hhslM