Really stupid question!

I know this sounds really stupid to all you tech savvy people, but I have a problem. How do I take a screen shot?

There should be a key somewhere in the upper right corner of your keyboard that says something along the lines of "PrtSc" (as it does with mine).
If you're using a laptop, it's very likely that it'll be printed on the key, along with another command. If the print screen command is underneath another one, or if it's smaller, then you'll have to press Fn+PrtSc otherwise just press the key. After that, go into paint, Edit>Paste. :)

Thanks Draco. I know it was a stupid question, but I really did need a pic of something and had forgotten how to do the print screen thingy! :)

No worries! And it ain't a 'stupid question' :)