To use screenshot the whole screen takes a screenshot of your entire screen, current window only takes only the current window and capture an area of the screen lets you select an area interacetively. There is also a delay for the screenshot you can set like a timer for a camera in the bottom right corner of the screen.
To launch screenshot from the menu -> Grapics -> Screenshot or run lximage-qt -s from the command line. Pressing the printscreen key also brings up the screenshot dialog.
