Screenshot is done by using the "Prnt Scrn" button.
If you have Windows 7 or 8 there is a program called "Snipping Tool" in which you can select what portion of the screen you want to make into an image. It then can save the file right to a JPG image.
and if you have a Mac you should know how to do this, but just in case, the hint is "shift command 3" for full screen, or "shift command 4" to select the area.
Just use the snipping tool. It's built into windows. The icon looks like a scissors. If it doesn't show up in your task bar, just search for snipping tool.