I got this picture from a google search but i have filled in for you.
Then go to http://www.whatsmyip,org and it will say "Your IP Address is XXX.XXX.XXX.XXX"
Give you friends "Your IP Address is XXX.XXX.XXX.XXX" then the port so e.g 33.33.33.33:22003
Or take a look here....
http://portforward.com/english/routers/ ... A_R1.0.htm
http://portforward.com/english/routers/ ... ftAuto.htm
http://portforward.com/english/routers/ ... t_Auto.htm