If you're asking about "SnippingTool.exe" that's included with VISTA and up, you'll find it in "%SystemRoot%System32"; you should make a shortcut of it and place it into your Quick Launch Toolbar Bar for quick access anytime. If you run across something onscreen that you'd like to save as a graphic format file (the SnippingTool can save your capture as *.PNG, *.GIF, *.JIF, or *.MHT), activate SnippingTool by clicking on the shortcut button you just added to your Quick Launch Toolbar Bar, choose the shape of the snip, set your clip boundary and once you release the on your mouse your capture will be in the snip tool, ready for further processing. Simple and quick! Good luck!
PS - As with most any utility, there are hundreds to choose from (most free) and most users will find one that they feel is exactly what they've been looking for, even though what they may have been looking for has been on their system all along! :P