Updated, October 19, 2012: Replaced Windows 8 Consumer Preview screenshots with those from the final version of Windows 8.
Without a Start button, properly shutting down Windows 8 can be a bit of a chore. If you want to shut down or reboot your Windows 8 PC by just clicking on a tile from the Start screen or a shortcut on the desktop, here's how:
Step 1: Right-click on a open area of your desktop, then go to New and select Shortcut.
Step 2: In the location box, type shutdown /p to shut down Windows 8 immediately or shutdown /r /t 0 to reboot Windows 8 immediately. Click Next to continue.
Step 3: Type a name for your shortcut, then click the Finish button.
Step 4: Right-click on the shortcut from your desktop and select Pin to Start.
Step 5: Go back to the Start screen and verify that your new shutdown tile appears.
That's it. Now when you want to shut down or reboot Windows 8, you can just double-click on the desktop shortcut or click the Start screen tile. Be sure to check out the rest of CNET's complete guide to using Windows 8.