Documentation or tutorials for lobby system?

I want to make a common multiplayer game lobby system, where players can join lobbies without having to travel to any new map. Once everyone is in a lobby together, the host/owner can enter the map with everyone and start the game.

Normal sessions don’t work here because they require members all to travel to a new map together when they join. But I’ve heard that you can join lobbies without having to travel anywhere immediately.

The problem is that there’s really no documentation on how to implement lobbies, and I can’t find any tutorials or guides online. Most videos or articles that say they implement “lobbies” are actually just implementing sessions and using an entry map, which isn’t what I want to do.

Does anyone know any good place to learn how to use lobbies?

Thanks in advance!