With the introduction of Mac OS X in 2001, Apple finally offered a true multi-user operating system. By configuring multiple users, you can restrict access to certain files and programs for other users if you need to. For multiple advanced users sharing the same Mac, you can create different user accounts so that you can each have your own shortcuts, music and photo libraries, and other preferences.
Go to the "Apple" menu and select "System Preferences..."
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Click the "Accounts" icon. This brings up the "Accounts" window. Click the gold lock icon in the bottom left-hand corner of the window to make changes. Enter your user password and click "OK."
Click the "+" button to add a new user. Type in information for the new user's "Name:", "Short Name:" (for network identification purposes), "Password:", "Verify:" and "Password Hint:" fields. Click the check box next to "Allow user to administer this computer" if you would like the new user to have administrative access. Do not check if you want the user's access limited.
Click "Create Account."
Decide whether you want automatic login turned on or off. Click "Turn Off Automatic Login" to bring up a choice of users when the computer boots up. Click "Keep Automatic Login" if you want to log in under the primary user account and switch users manually. Close the "Accounts" window.
Go to the "Apple" menu and select the "Log Out Your User Name..." menu command. The exact phrasing of the command varies according to which user is logged in. Click the "Log Out" button.
Do not click the "Allow user to administer this computer" box if you're creating a user account for someone who shouldn't be allowed to modify your system preferences.
Click the "Parental Controls" tab in the "Accounts" window in between steps 3 and 4 if you want to configure program options for a child or teen user.
Mac OS X creates a new user folder for the new user with different "Documents," "Library," "Movies," "Music," "Pictures," "Public" and "Sites" within that folder so the new user's stored files are different than the primary user's.
Creating a new user resets the applications in the OS X dock to the default settings. The new user will have to add his own application shortcuts.