On that page, click the "+" symbol in the upper left side to reveal the Port Forward table, then fill in the appropriate fields:
Private IP- this is the IP address on your network, from the DHCP table
Private Port – this is the TCP/UDP port that the device is using. In this case, the computer at 10.0.0.11 is using port 5900 for “VNC” (so I can use my desktop computer over the Internet), while the AyrScout camera at 10.250.250.84 has a normal web server at port 80. Web servers (devices you access using a browser) usually are on port 80.
Type – TCP or UDP – choose TCP if you're not sure; UDP may be better for file-sharing devices and others.
Source IP/mask – Usually leave blank to allow access from anywhere on the Internet. If you only want to ONLY let a select IP address to use this device, fill it in here with an appropriate mask.
Public IP/mask - Leave blank
Public port – the port you want to “expose” to the outside world for this service. In this case, I'm exposing my desktop computer's VNC server as port “7001.” DO NOT USE any port lower than 1000 or ports 9001 to 9999 – these are reserved for Ayrstone equipment.
Comment – useful for remembering what you have set up.
Enabled – check the box to enable the port forward.
Click Add to the right of the Port Forward line
When you have added the port forwards, Click the Change button at the bottom of the page, then the Apply button at the top of the page.