This is one of the helpful tool. The shortcut Keys to take a full screen snap is "Volume - Down" + "Power Button"
To take a screen shot of an area or to select a range its handy to use the "Screen Shot" option from the menu short cuts
You can re-size the area and use "Share" to share instantly through any other supporting applications (such as, Whatsapp, instagram, Flicker and etc)
"Crop" will save the area as an image on your "screen shot folder"