One MineOS installation can in theory run as many minecraft servers you like, if you have hardware strong enough, and you can compile yourself a version of the utility “screen” that is not hard limited to 40 sessions. A standard MineOS installation is thus limited to max 40 servers, if you have enough memory and processors available.
To run more than one server you need to give each server its own port number. If you look at the server.properties you will see a setting that say “server port” that default is set at 25565. This is also the standard miencraft port so any game connections tries that port if nobody tells the game otherwise.
So to have another game server, you need to use another port number, for example 25566 (one number up). You players then need to tell the game to connect to another port. They do that by adding (in this example) “:25566” behind the server address. Note the " : "
This only helps you on your LAN (home network). If you want to allow them in through the internet, you need to set up “port forwarding”. Take a look at this page to research this, and possibly find a howto for your internet router. : https://portforward.com/