this is tricky since every router is going to have its own ui and layout.
(heres a screen of my current rulset)
http://imgur.com/ff3ubJc
(and heres a bonus picture of my LAN)
http://imgur.com/r8wQkbh
in anew browser tab, navigate to this address.
192.168.1.1
This will allow you access to your router, from here you will be looking for 'wan settings' or 'virtual server' it might have a few different names.
You want to find a section that will usually be labled 'port forwarding' or 'virtual server' you should now see a few empty boxes for you to fill out.
Service name: give a name to your new rule, maybe add the name of the game that this rule is for to keep it easy.
port range: this is the ports that you want to be opened, for example, port 3074 would go in the field.
local i.p.: here you put in the computers address that you want this rule to apply too. you would put your computers static i.p in this field.
local port: you don't need to worry about
protocol: UDP or TCP, usually you want to use Both if available, or unless otherwise mentioned.
Ifi you can't make sence of my rubbish, try this webpage. it helped me alot way back in learning how to port forward, so I could host online games for friends.
http://portforward.com/
Hope that helped a little.