How to Shut down a computer

Turning off means that Windows closes all open programs and document, logs all users off and then completely turns off your computer. To start your computer again, you will have to press your computer's power button.

Restarting your computer means that computer closes all open programs and documents, logs all users off and then shuts down and starts Windows 7 again, so that you will see Welcome screen again.

Stand by means that computer turns almost all its power off to save battery or energy. This does not mean that computer is completely turned off - all information about the running programs is retained in computer's random access memory (RAM, aka memory, read about Hard disks and Memory here). You can resume from standby by pressing computer's power button once and you will have all your running programs back on your monitor within seconds.

Turning off or restarting Windows 7 computer

To shut down or restart your computer, open Start menu by clicking the Start button or pressing Windows Key (or Ctrl+Esc) on your keyboard. Then click Shut Down:
Windows 7 Start Menu, Shut down button chosen

Windows 7 will not confirm the action, so please be careful clicking the button! After you click Shut down, Windows 7 will immediately close all open programs, log you off and shut down your computer.

If you want to restart your Windows 7 computer, open Start menu and click the right arrow button to the right of the Shut down button. In the list, click Restart.
Windows 7 Start Menu, arrow right button to the right of Shut down button opens a list of other actions. Click Restart if you want to restart your computer.
Turning off or restarting Windows 7 computer without logging on first

You can also turn off or restart your Windows 7 computer when Welcome screen is displayed. Click on the red power button in the right lower corner to shut down your computer immediately:
Windows 7 Welcome Screen, clicking on the red power button shuts down the computer immediately.

If you want to restart, hibernate or put your computer to sleep instead, click the up arrow button to the right of the red power button.
Windows 7 Welcome Screen, click on the up arrow button to the right of the red power button to see other Shut down options, such as Restart, Sleep and Hibernate.

Click on the desired action in the list (this picture does not show Sleep and Hibernate options, but they are available on most modern computers):
Windows 7 Welcome Screen, Shut down options list after clicking on the up arrow button to the right of the red power button. Click on the desired action in the list.

Sometimes the red power button has a yellow shield icon on it and the menu includes an additional command - Install updates and shut down. This command would download all updates available, install them and then turn off your computer.