On the "Virtual Service" tab, enter the IP address of the computer on your network that is hosting the service (game or whatever). Enter the port number (or port range) that outside users will use to access the service. And enter the port number (if different) that the computer on your network is using to host the service.
Actually, that "Apply" button it's for the "Items show in every page" setting.
I'll try UPnP, thanks.