To lock the screen, perform one of the following actions:
Choose Actions -> Lock Screen.
If the Lock button is present on a panel, click on the Lock button.
To add the Lock button to a panel, right-click on the panel. Choose Add to Panel -> Actions -> Lock.
When you lock your screen, the screensaver starts. To unlock the screen, move your mouse to display the locked screen dialog. Enter your username and password in the locked screen dialog, then press Return.
For information on configuring your screensaver, see Using Preference Tools.
To lock your screen correctly, you must have a screensaver enabled.