How do I make players spawn in a lobby and then go to a map, and then go back to the lobby?

I'm making a game, and I've got maps, but I do not know how to make the players who spawn in the lobby go to the map when the round begins and then go back to the lobby when the round ends. Please help me. Thanks.

I'd suggest to spawn them inside the lobby,Place a SpawnLocation. To teleport them to the map you'd commonly use the MoveTo() function,Wiki link : http://wiki.roblox.com/index.php?title=MoveTo_(Function)

Even to teleport them back you use the MoveTo() function.