If you see something interesting on your screen and you want to take a screen shot, hold down the Windows Key, press the PrtScr key. The screen shot is captured to the clipboard for pasting into your favorite graphics or image editor, but it’s also saved automatically to your My Pictures folder with the name Screenshot.png. The next time you do this, it will be called Screenshot(1).png, and the next time, Screenshot(2).png, and so on.
You don’t have a lot of editing options, nor can you capture just part of your screen this way, but you can sure save screenshots quickly and automatically. And what the heck, you can always open them from My Pictures folder and edit them and change their filenames.