Wild guess, but if you are running a Windows OS (not sure if it's the same or not with any other OS),
Push the PrintScreen button near the top right of your keyboard
Once done, open Paint and push CTRL + V on your keyboard to paste your Screen Print to Paint and save the file.
Best of luck,
--FireHazard772
EDIT: Also, if you have Windows Vista or 7, you can use the program "Snipping Tool" to 'cut out' a piece of what is showing on your screen, rather than just showing everything that is up/running.
To access Snipping tool: go to Start Menu - Programs - Accessories