Are you talking about a "Server"?
Such as a "server" hosts the game. If so see below, otherwise give us some more information
You will need to either somehow keep the game running (so that people can join) or if you have some advance web programming / OS skills you could create a Scheduled Task (Windows) that checks a database for anyone wanting to play and start the game up for them (one instance at a time).
The other one would be the same as the database but Only start the game if someone wants to play. If the instance is already running show that the game it going and let them join.
