That means:
go to Start -> run and type "cmd" (no quotes).
You have opened a command prompt window (old DOS style).
Type the command
ipconfig and hit return. You'll get something like this:
Microsoft Windows XP [Versione 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
Configurazione IP di Windows
Scheda Ethernet Connessione alla rete locale (LAN):
Suffisso DNS specifico per connessione:
Indirizzo IP. . . . . . . . . . . . . . . . : 192.168.1.150
Subnet mask . . . . . . . . . . . . . . : 255.255.255.0
Gateway predefinito . . . . . . . . . : 192.168.1.1
.............other stuff deleted............
Your IP is (in this case)
192.168.1.150
Your router's IP is (in this case)
192.168.1.1
Open a browser window and type your router's IP in the address bar, like:
http://192.168.1.1
hit enter
you get to your router's login page.
go to
http://portforward.com/ to find out wich user and password you need to enter, it depends on the make and model of your router.
It could be something easy like "user", "user".
You might need to "open" (forward) a port on your router...
Tell us which menus you see in the router's management window and we'll take it from here.