...

1. From the Apple Menu, select system preferences (or use the system preferences icon on the dock).
2. Select  "Security & Privacy."

Enabling the Firewall

1. Select the "Firewall" tab.

2. Click the "Turn Firewall On" button.

    

   Note
   title Unable to turn on your firewall?
   Make sure the screen says it is unlocked for changes.  If not, click on the lock icon to unlock the settings (you may be prompted for the administrator password).

3. You will now see a screen indicating that the firewall is turned on.
4. Click on the lock icon to lock down the settings.