This shortcut closes your currently open window, not the entire program. We use keyboard shortcuts every day to save time and bother - here some of our most-used shortcuts. There are times when it's just easier to tap a few keys on a keyboard rather than fiddling about with a mouse.
(Keyboard image by Jeroen Bennink, CC BY 2.0) Here are the ones we've found most useful in our day-to-day lives. There are keyboard shortcuts for pretty much everything you regularly do on a computer.
