How to find the IP address of my computer

Each machine connected to a TCP/IP network is assigned an IP address; this we already know. It's not that difficult to determine what that IP address is.
In versions of Windows from Windows 2000 and later, run the Windows Command Prompt (Typically in Start, All Programs, Accessories). In the command prompt, type IPCONFIG and you'll get something similar to this:
Start .>  Run > CMD >ipconfig

Connection-specific DNS Suffix . :
IP Address. . . . . . . . . . . . : 192.168.1.5
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1

"... since I'm behind a router, this is not the IP address that will actually be used when I access the internet."

As you can see, the IP address of this computer is listed as "192.168.1.5".