From Worldstart Tips: (While I don't use Win 8, I hadn't heard of this before)
Windows 8 includes a fantastic feature to take screenshots (images of what’s on your screen) quickly and easily. Traditionally, to take a screenshot in Windows 7 and below, you would need to hit the PrtScn key, then open a photo program like Paint or Photoshop, and go to Edit > Paste (or Ctrl + V) and save the image.
On Windows 8, you can simply hold down the Windows key (the windows icon on the keyboard next to the Ctrl key) and hit PrtScn, and a screenshot will be saved to your My Pictures\Screenshots folder as a PNG format image. This popular image format can be read by windows and by most photo software.
So next time you want to show somebody something in Windows 8, or save an error or warning that comes up on the screen, hit the Windows Key + PrtScn key and you’ll have a screenshot saved for you.
P.S. For detailed instructions on how to take a screenshot in other operating systems, check out http://take-a-screenshot.org/