Well it depends if you are using a MAC or a PC. I use a PC and for PC's you just hit the Print Screen button then go to "Paint" on your accessories, then paste, then save, and when you save change the file type to JPEG.
I believe "print screen" is a windows only option. The keyboard commands for Macs are different. It doesn't matter if it's Mac or PC the abilities are limited. There are programs you can buy/have that will allow you to take pictures of your whole screen, or selected areas, and add detail like circles, arrows, highlights, etc. Honestly the paid programs for screen shots work better then the keyboard commands that are very limiting. My OS (operating system) is Ubuntu (Linux) so I use a free program called Shutter to take my screen shots. For PC (windows) you can buy Snagit. I'm not sure what the equivalent is for Mac!
Top right hand corner of your keyboard is a key that say "Print screen", hit that and then it will paste wherever you want it to... if in an e-mail just paste it. If you want to save it to your computer you can put it into paint shop and then save it. :)