Take Screenshot is probably one of the simplest, most managable and quick tools you can find to take screenshots of what you see on the screen.
Take Screenshot lets you select the area of the screen you want to capture (by default it captures the whole screen), and once selected, it saves it in JPG. It is ideal, above all when you have to take many shots, as it takes them one after the other and very quickly.
Take Screenshot, apart from being very easy to use, is also totally free.