Answer:
It can't. Linux is essentially what makes you able to run your computer. It is the kernel of your operating system, shutting it down would be done by shutting your computer down(init 0).
Many window managers and all popular desktop environments allow you to shutdown the computer from the GUI (if that is what is meant by 'closing' linux). The specific procedure will depend on the GUI, but it is usually obvious, like click on some menu and select shutdown.