Have some faith... if the answer was right around the corner I wouldn't bother posting.
Oh... really... lol:
how does nikon cls work - Google Search
YouTube - nikon cls system
Flickr: Search for a group
And there was the link that I provided. If it was for a friend, did he not have the manuals? I have an answer for that too.
The manuals from every Nikon product from the 70's to the present:
Download-Center
Rather than have us cut and paste info from these links, it would be courteous of you to have gone there directly or helped your friend go to these links him or herself.
If you have a specific question, I am comfortable with CLS and would be happy to answer. Asking us to write a book on the basics of how it works... THAT is lame... and a little lazy. The answer is there, if someone doesn't want to click a few links and read there... wow, thats sad.