If you're using Windows 8, here's how to have the Snipping Tool readily available when you next want it:
Press the Windows key and Q together, to bring up a list of all the apps on your computer.
Look for 'Snipping Tool' and RIGHT-click on it.
Look at the the bottom-left of the window for 'Pin to Taskbar' and click on it.
You'll then have a Snipping Tool icon on the Taskbar at the foot of your screen.
In future, when you want to capture all or part of your screen, simply click on that icon. You can then use your mouse to draw a rectangle around the area that you want to capture (by holding down the left mouse button as you do so). You can then save it by going to File > Save As. (Choose a name for your file and ensure that 'File type' is set to 'Jpeg'). Easy peasy!