The easiest way to shutdown your computer is to press ctrl+alt+delete.
A window will appear and you will see several useful options.
Click on the Shutdown option. You will see three more options come up.
The option you want to choose is Shutdown and Reboot.
This will close all of your programs, log you out of the computer, cycle the power on the computer, and bring it back up to the login screen.
You can also access this option by clicking on Start, Shutdown, and choosing the option to Restart from the drop down list.
This is the preferred way to shutdown your computer at the end of the day as it logs you out of the computer, clears the system memory of any errors that have developed over the course of the day, and leave the machine ready for you to login immediately the next day. It also allows any needed updates to install automatically over the course of the night.
If you do not log out at the end of the day, the next time you use the computer you will not be able to access your network data or printers until you reboot (all users are automatically logged out of the network before backups are run each night).
If you only choose the option to logout and login as a different user every night errors build up in the system over time and cause the computer to work much more slowly and in some cases fail.
If you choose the option to Shutdown the computer and do not turn the computer back on, you will have to wait for the computer to boot up, and apply any updates that were set to run over the course of the night. Our computers are set to enter power saving mode after 30 minutes of inactivity so they do not waste power when they are not being used.