How to make a multiplayer lobby?

I followed this tutorial to make a multiplayer lobby Making a MULTIPLAYER Game? Join your Players with LOBBY! - YouTube but I’m confused as to how to actually start the game from this screen. I want the host to immediately go to the game scene when they create a lobby and to wait for other players to join that way. How can I accomplish this? Explain like I’m five, I’m very new to netcode.

edit: in particular I’m confused about how to make clients join a certain host. I’ve managed to make a simple scene where players can move around and chat in a chatbox, but I don’t know how to handle multiple hosts. Any information you can provide is appreciated!

The question is, are you new to coding? If so, you’re starting with something that’s incredibly hard to swallow, even for people that has a few years of experience. Multiplayer is HUGE and complicated, and a giant task if you want to do this alone. Protip, start small. (Sorry for not being able to help with this)