I'm guessing you need to set the router to forward one or more ports, and / or set for a virtual server. By nature, any router will keep outside computers out. You need to allow these outside users access to the host of the game. This means setting some ports to be forwarded to the host so it can get them.
If what I'm saying seems hard to grasp, then you need to study the router documentation for how to host a game for computers outside your local network.
Bye.
