How can I use TeleportPartyAsync() to get a group of players standing on a part into another place?

I've been trying to use TeleportToPrivateServer() and messing around with ReservedServers all day, and I still haven't found anything useful! Could somebody please, help (please explain too, don't just write the script - I want to learn!) me create a script which teleports any players touching the part into a private server / reservedServer to stop players joining mid-way through a game? This would be much appreciated ! :)