In Windows 8, Microsoft has buried the option to shut down in the Charms bar. If you're running Windows 8, this is likely to be one of several gripes you have with the new OS. See also: Windows 8 review.
There are various methods by which you can make your life easier, from creating a shortcut on the new Windows 8 Start screen to installing the free Start Menu 8 utility.
However, there's an even easier way which will take you less than 30 seconds to configure:
1 - When on the Start screen, begin typing 'Control panel'. Click it in the list of results which appear.
2 - In Control Panel's search box, type 'power'. Under Power Options, click 'Change what the power buttons do'
3 - By default, 'When I press the power button:' is set to Sleep. Simply change this to Shut Down. If you have a laptop, you can choose separate behaviour depending on whether it's running on battery power or connected to the mains.
Now, instead of using your mouse to shut down your computer, you can quickly press the power button to achieve the same thing.
Of course, if you're happy to leave your PC in sleep mode, you don't need to configure anything at all. Simply get into the habit of pressing your PC's power button instead of clicking through the Charms bar for the same option within Windows 8. If you have a laptop, you can merely close the lid to put Windows into sleep mode, but using the steps above you can change what that action does, too.