Maximize your workspace with extended desktop mode, which lets you enjoy full-screen apps and windows on each monitor. Then, use Mission Control to organize apps and windows across your displays. If your Dock is on the bottom of your screen, it appears on any of your displays when you move your pointer to the bottom edge of your display.
Turn on extended desktop mode
Make sure that your external display is powered on and connected to your Mac.
Choose Apple () menu > System Preferences, then click Displays.
Select the Arrangement tab.
Make sure that the Mirror Displays checkbox isn’t selected.
Arrange your displays or change your primary display
So that you can move apps and windows across your displays in one continuous motion, arrange your displays to match the setup on your desk. You can also change your primary display, which is where your desktop icons and app windows first appear. Here's how:
Choose Apple () menu > System Preferences, then click Displays.
Select the Arrangement tab.
Arrange your displays or change the primary display:
To arrange your displays, drag one of the displays where you want it. A red border appears around your display as you arrange it.
To change your primary display, drag the white bar to another display.
