How to Disable Mirroring on a MacBook

Connect the external monitor to your MacBook using the appropriate cable. For example, If both the MacBook and the external monitor have VGA ports, use a VGA cable to connect the two devices.
Click the 'Apple' icon in the upper left corner of the desktop and then select 'System Preferences' from the drop-down menu.
Click 'Displays' in the Hardware section and then click the 'Arrangement' tab.
De-select the 'Mirror Displays' check box in the bottom left corner of the window.
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