Open a web browser like internet explorer or Netscape. Enter the ip address of your router in the address bar of your browser. By default the IP address should be set to 192.168.1.1.

You should see a box prompting you for your username and password. Enter your username and password now. By default both the username and password are blank. Click the Ok button to log in to your router.

Click the Firewall button near the top of the page. Use the Protocol drop down box to select the protocol type of the ports you are forwarding. If you are forwarding a single port, enter that port number into the LAN port range, Left WAN port range and the Right WAN port range boxes. If you are forwarding a range of ports, enter the lowest number of that range into the LAN port range, Left WAN port range box. Then enter the highest number of that range into the Right WAN port range box. Enter the IP address to forward these ports to into the LAN IP Address box. If you are forwarding ports so you can run a program on your computer, you should enter your computer's ip address into that box. When you are finished, click the Add button.

When you're finished, click Save near the bottom of the screen to save your changes.

And that's it! You're done! Hope this helps.