To password-protect your account on Mac OS X (10.5-10.7), follow these steps:

1. From the Apple menu, click System Preferences.
2. In the System Preferences window, click the Accounts (10.5-10.6) or Users & Groups (10.7) icon in the fourth row, highlighted in the following graphic:
   
3. You will see the Accounts (or Users & Groups) window, which should look similar to the following:
   
4. If the lock icon in the lower-left hand side of the window is locked, click it to unlock it.
5. At the bottom of the left-hand column, click Login Options.
6. Confirm that Automatic login is Disabled (OS 10.5) or Off (OS 10.6 and 10.7).
7. Click the lock in the lower-left corner of the window to prevent further changes. The window should now look similar to the following:
   

8. NOTE

   If you want to make changes to these options in the future, you must click the lock in the lower-left corner of the window and type the Admin password to unlock the page to access these options.