- Go to http://192.168.2.1/ in your browser.
- On the sidebar, move down to Firewall>Virtual Servers.
- Here it asks you for the router's admin password. This is not the same thing as the WiFi network password. If you don't know what it is you probably haven't set one, so just click Submit.
- This is where you open ports. You'll need a static IP on the internal network to open ports to a particular machine. There are some suggestions at the top but some of these are outdated.
Generally, a better solution is to use UPnP (if it is supported by the server you want to use), which is enabled by default.