Welcome to Gaia! ::

If you have a PC,
Press the "Print Scrn" button on your keyboard.
The screen image will be copied onto the clipboard.
Open any art program such as MS Paint.
Paste the image.
You now have a screenshot! You can crop, edit it, add caption, etc.
Save in your favorite file format (.jpg, .png, w/e)


If you want to share the screenshot with others,
get an account on an image hosting site if you haven't already.
Some popular options are photobucket.com and imageshack.us which are both free.
Upload the image onto the hosting site.
When posting, you can see the IMG / Imgleft / Imgright buttons above the text box. These are to help you create the code to post the image.
Example:


and your pic should appear.

I crop and edit images on paint, usually, and they're of adequate quality for most purposes (such as showing an inventory of items for sale, showing a trade or a PM from another user, etc.).

If you have a Mac, you can use the following instructions to take a screenshot:

• Command-Shift-3: Take a screenshot of the screen, and save it as a file on the desktop
  
• Command-Shift-4, then select an area: Take a screenshot of an area and save it as a file on the desktop
  
• Command-Shift-4, then space, then click a window: Take a screenshot of a window and save it as a file on the desktop
  
• Command-Control-Shift-3: Take a screenshot of the screen, and save it to the clipboard
  
• Command-Control-Shift-4, then select an area: Take a screenshot of an area and save it to the clipboard
  
• Command-Control-Shift-4, then space, then click a window: Take a screenshot of a window and save it to the clipboard

I use a PC, but I hope that information is useful to someone!

Misti