System shutdown brings the system to a condition in which it is safe to turn off the computer. All file-system buffers are flushed to the disk, then a message box is displayed informing the user that the computer can be turned off. There is also a reboot option that will restart the computer, rather than display this system shutdown message box. For more information, see How to Shut Down the System.
Logging off stops all processes associated with the security context of the process that called the exit function, logs the current user off the system, and displays the logon dialog box. For more information, see How to Log Off the Current User.
Locking the workstation protects the display from unauthorized use whenever you leave your computer. To unlock the workstation, you must log in. For more information, see How to Lock the Workstation.