If you want to take a screenshot of your entire Ubuntu desktop, simply follow these very easy instructions. Once you have your desktop arranged and ready for the screenshot, hit the Print Screen button. The label for this button on your keyboard will sometimes be abbreviated to a shortened version, such as "Prt Scr", or something similar.
Once you hit the button, a dialogue will come up, with a thumbnail of your image in it, asking you which directory you'd like to save your screenshot in. Choose your favored directory, then simply click the save button in the lower right corner of the dialogue. You now have your screenshot!
If you'd like to take a screenshot of only one single particular game window, make the game window your active one, and click both the ALT button and the Print Screen button at the same time. The dialogue will come up with a thumbnail of only that single, active window. Follow the same steps as above for the desktop screenshot. And, now you'll be able to take that awesome screenshot of your favorite MMO game and put it online anywhere you would like.
This is the beauty of Ubuntu Linux, something like taking a screenshot in Ubuntu Linux is so incredibly easy and straightforward, while in Windows it is a convoluted chore, with extra unnecessary steps and complications. Can you tell that I'm a Linux fanboy? This also makes taking game screenshots even easier and fun.