When you're done working on your computer for the day, you probably close each open application one by one. If so, chances are that you've wished that you could close all you open applications at the same time.
To do so, hold down the Ctrl key and click on each application button on your taskbar. Once you've selected all the application buttons on the taskbar, right-click on any one of them and select the Close Group command from the shortcut menu.
If you have any application in which an open file hasn't yet been saved, that application will prompt you to save the file.