Choose Apple menu > System Preferences, click Users & Groups.
Click Login Options.
Click the lock icon to unlock it, then enter an administrator name and password.
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Click the button next to Network Account Server.
The button is labeled Join if you haven’t already connected to a network account server. It’s labeled Edit if you already have an existing connection.
If you clicked Edit, click Add .
Enter the fully qualified domain name of a network account server in the Server field, or choose one from the Server pop-up list.
To add another server connection, click Add , then repeat steps 3 and 4.
Click OK.
If your computer name contains a hyphen (-), you might not be able to join a network account server. To check your computer name, and change it if necessary, use Sharing preferences.
Choose Apple menu > System Preferences, then click Sharing.
Reference: Apple.com