PLEASE READ: this game is 2 - 20+ players, but it's not something you can play alone.
PLAY OVER LAN: start the game as a host, other players will need to join on your internal ip (like 192.168....) using the port number you selected.
PLAY OVER INTERNET: host will need to open the port they choose to use on their router. Without forwarding the port, other players won't be able to connect using your external ip.
(Ask me how to do this if you're not sure)