Newbie to Comodo Firewall With a Question

I am trying to set up a game (Diamond Mind Baseball) so that another person (PC) can connect to mine so that we can play head to head.

I have a specific port number that DMB uses and that needs to be opened so that a connection can be successfully made.

My question is what do I have to do, and equally important – how do I do it! – to get the Comodo Firewall to accept another PC through a specific port to connect to my PC???

Any help would be MUCH appreciated!!