Single button TD. 'Print Screen' just next to the F12 top row.
This puts the current screen into the clipboard (everybody has one, don't worry where it is). Open an imaging program, click file , new then edit, paste. Voilą ! Save it as ' whatever.jpg ' and you're done. (Caution - for some reason saving as a .bmp doesn't work for me, comes out monochrome).
If the window you want to capture is smaller than the screen size, use Alt and Print Screen buttons simultaneously.