If you're a long-time user of Windows, you're likely fully aware that PrintScreen captures a screenshot of everything on your screen. But what if you only wanted a section?
Well, with Windows Vista and 7 there's the snipping tool. Vista will only have it if you have the Tablet PC Optional Components feature installed, and then will be found under Start menu -> Programs -> Accessories. Windows 7 is a lot easier — you can just hit the windows button and start typing "snipping tool" until it appears.
Once the app has loaded, if you press the down arrow on the New button you'll get a few options for taking different kinds of screenshots — Free-form, Rectangular, Window and Full Screen. You can then save to multiple formats, and draw over the shot with a pen or highlighter if you desire.