On Apple computers, you use the Command button, the shift button and either the number key 3 or 4. If you use Command+shift+3, it will take a whole screen grab, or if you use Command+shift+4, you can control how much of the screen you'd like to take. The screenshots will automatically upload to your Desktop.
To create a screenshot on an Aspire One PC click the little button marked PrtSc in the upper right-hand corner.
If you are using a Mac you hit Command+Shift+3 (or 4). If you use 3 it will take a picture of the entire screen, but if you use 4 you can highlight a certain part of the image that you would like to capture.