Locking the screen prevents access to the applications and information, allowing you to leave the computer unattended. While your screen is locked, the screensaver runs.
To lock the screen, perform one of the following actions:
Choose System → Lock Screen
Click the Lock Screen button, if it is present on a panel
To unlock the screen, move the mouse or press any key, type the password in the locked screen dialog, and then press Return.
If other users want to use the computer while it is locked, they can move the mouse or press a key and then click Switch User. The login screen is displayed and they can log in using their credentials. They will not be able to access any of your applications or information. When they log out, the screen is locked again and you can access your session by unlocking the screen.