Completely have no clue how to do it, do I connect my steam account somehow?

Not sure if you can do it from a stand alone version. If you downloaded it on steam it should automatically link when you logon on that version

I should be connected if you're using the same account login details for toribash and the toribash forums.
Once you download and login to toribash and play a multiplayer match everything should work just fine.

Assuming you're asking if you can log in with your Steam account - no. You have to use a Toribash account which is the same for forums and for the game.