Taking a screenshot is a common task with computers.  Sometimes referred to as a screen dump, snapshot or screen capture – a screenshot is an image that is created from a software program or the operating system.  It allows you to capture an image of what your computer screen (or just a section) looks like at a given point in time and then send that image to others, it can be saved as an image file such as a GIF or JPEG, manipulated, or printed.

There are several ways to capture a screenshot, often each of these methods depend on what computer operating system you are using and what you intend to take a screenshot of. Below is a listing of all the different ways to create screenshots.

Microsoft Windows users and most other operating systems:

The simplest way to take a screenshot is to press the print-screen (sometimes shortened to PrtScn or something similar) key on the keyboard.  This takes a screenshot of the full screen and places it into the computer clipboard (temporary memory). Once in the clipboard, paste that screenshot into Microsoft Paint or other image editor.

Tip Pressing and holding the ALT key while pressing the print screen key will take a screenshot of the current active window, instead of the full screen.

Tip Microsoft Windows Vista (not home basic) and Windows 7 users can use the Snipping Tool (Start -> All Programs -> Accessories -> Sniping Tool)  to more effectively take screenshots.

These are some more detailed instructions:

1.  Set up the screen the way you want it.  Remember that unless you use Alt + Print-Screen (which captures only the current Window) the WHOLE screen will be captured so it will save the task bar and any other things you can visually see on your screen.

2.  Press the Print-Screen key on the keyboard to capture the image.  Often nothing visual will happen at this point.

3.  Open up an image editor or another program that can support images (Microsoft Word or many email applications will work fine).   If you’re not sure what to use, use Microsoft Paint (Start -> Programs -> Accesories -> Paint).

4.  From the ‘Edit’ menu, choose ‘Paste’ or press Ctrl+V as a shortcut.

5.  Save the image and then either attach it to an email or print it out depending on what you need to do with it.

For more Information:
http://take-a-screenshot.org/
http://www.wikihow.com/Take-a-Screenshot-in-Microsoft-Windows