usually when I'm on mail or facebook, my friends post a picture of what there on on the computer, but how do you take a picture of the website your on?

If you're on a PC (not a Mac), hold down the Fn key (lower left) while you press Prnt Scrn. That copies what's on your monitor to the clipboard.

Then open an email document or a Word file or whatever you want to save it to, and press Ctrl + V (to paste).

does it work on a laptop or only a PC ???

It'll work on a laptop or on a desktop that is a PC, not a Mac. I'm sure there's a similar series of keys on a Mac, but I don't know what they are.

I tried but nothing happened.

What did you paste it into?

http://www.google.com/search?q=how+to+print+screen&rlz=1C1GGGE_enUS379US379&oq=how+to+print+screen&aqs=chrome.0.57j60l3j62l2.3179&sugexp=chrome,mod=1&sourceid=chrome&ie=UTF-8

I'm using Windows 7. What does your computer use?

That page was helpful but where is my clipboard?

It's inside your computer. It stores only one image at a time, so as soon as you copy something to it, you'll need to paste it into something else. The next time you copy something, it'll delete whatever's left over on the clipboard.

Is it in my document, libraries, computer?

The clipboard is not a program or a file in itself. You cannot locate it on your computer. All you can do is copy stuff to it and then paste from it.