ok for people who want to forward a port so you can run a server of some sort its why some routers will call it virtual server or port forwarding/server or something like that.
First login to your router usually 192.168.0.1 or 192.168.100.1 you can see alot of different way and you can change this partially 192.168.135.100 or completley 55.345.123
all ips have a different class as class a or class b certain ones are used for certain types like for people needs alot of ips to there self or orgizination or there are none routable like the 192.168.0.1 just meaning you can use that ip on the internet it stays in your local network and not internet.
so maybe you want to use windows remote desktop from anywhere in the us you would do this by going into your router and going to the portion it says about port forwarding or server.
set port to 3389 for local and incoming and the ip address the computer you want to access from out side the router. now you can set up for multiple computers if you know how to change windows remote desktop to be able to send different and receive different port numbers
actually did a quick google search the know how is at
http://support.microsoft.com/kb/306759
awsome i didnt think they would have posted that but i figure someone would have the information posted
and to get remote desktop to send to a different port is you just put in the tragets ip and add :port
example 34.254.345:6789