On your router look for where the serial number is and it should list the model number. So you just need to grab your router's make/model and find it on that site. This site has a lot of different guides that show you with screenshots how to port forward on your specific model of router. So instead of trying to list out how to do this for every possible router out there (yeah right!) I will direct you to this handy site instead. Great now you're logged in! Now what? Well this is the part that I feel most people would get lost and this is also the part where most people's experiences will digress from each other as different routers have different menus and they don't alway use the same terminology for the same thing. Usually it is something really simple like Admin/Admin or Admin/Password etc.
If you don't know your login for the router you can always ask someone who does or google what the default username/password is for that brand of router that you have. This will take you to your router's web interface where you can login. So for mine it would be 192.168.1.1 and hit enter. Hey remember that default gateway number that you jotted down? Well now is the time to use it! Open your web browser and in the address bar at the very top type in that number.
