You can take screenshots on multiple ways.
2 ways I use:
1. When you want to take a screenshot press PRT SCRN (print screen) on your keyboard, it's next to scroll lock. Then after you finished open MS Paint and press CTRL + V now it appears on the screen, do with it what you want.
2. Download Xfire,
www.xfire.com, then put it on and go ingame. Now press SCR LK + S (scroll lock) you can take as many was you want with this one. When you quit the game a screen will appear and you can choose which ones you want to add and delete and you can even add a tiny explanation.