P2P multiplayer game: create a room

Hi everybody!
I looked at the very good tuto by @The_Gem_Dev about multiplayer and I think I get it.
But, I don’t understand how can you exchange the ID client easily (it is something like a dozen alphanumerical characters) especially if you don’t know who is connected to the broker server.

Is it possible to create rooms? Or just getting the list of who is connected to the broker server?

Thanks