To leave X, you need to use a menu. Unfortunately for beginners,
this is different for every window manager, and for most window
managers, it can be configured in many ways. If there’s an obvious
menu, look for an entry like “Exit” or “Close Window Manager.” If
you don’t see a menu, try clicking each of the mouse buttons on the
background of the screen. If all else fails, you can forcibly kill
the X server by pressing CTRL-ALT-Backspace. Forcibly killing the
server destroys any unsaved data in open applications.