Your Mac takes full advantage of each display that you've connected to it by providing options for using the additional screen space. Learn how to extend or mirror your work to an additional display.
You can set up an additional display with your Mac in several ways. You can connect a display in addition to the built-in display on your Mac. If your Mac doesn't have a built-in display, you can add a display to the first one you connected. You can also use AirPlay and Apple TV to mirror or extend your Mac desktop on an HDTV.
Set up an extended desktop to make one display an extension of the other.
Set up video mirroring to make the additional display show the same desktop and windows as your main display.
Set up closed-display mode to use your external display while the lid of your Mac notebook is closed.
When you use your displays as one continuous desktop, you can spread out your work any way you like. Move your pointer past the edge of one display and it appears on the other display. At first, your primary display has all of your desktop icons and open app windows. You can drag them to the other display as needed.
Connect and turn on your additional display.
Make sure that the Mirror Displays checkbox isn't selected.
Each display has a menu bar.
Each display can have full-screen apps. To take an app full screen, click the green button in the upper-left corner of the app window. Or press Control-Command-F.
You can use Mission Control to organize windows and full-screen apps across your displays.
If the Dock is positioned at the bottom of your screen, you can view it on any one of your screens by moving your pointer to the bottom edge of that screen.
You can tell your Mac where your displays are in relation to each other. Use this feature so that your connected displays match their real-world location when you move between windows.
The blue boxes in the Arrangement pane represent all displays that you've connected to your Mac. The size of each box represents the current resolution of each display. In this example, the smaller box on the left represents a MacBook display. The larger box on the right is the Apple 27" Thunderbolt Display.
To change the location of a display, drag its blue box to where you want it. For example, you might have an external display to the left of your MacBook in your workspace. If its blue box is at the right side, you can drag it to the left to match the actual location.
The white bar at the top of the blue box identifies your primary display. The primary display is where your desktop icons and open app windows first appear. To make a different display your primary display, drag the white bar to the box that represents that display.
Video mirroring shows the same desktop and windows on multiple displays at the same time. You can use it to view content such as photos or videos on a larger display or HDTV.
In the lower-left corner of the Arrangement pane, select "Mirror Displays."
In OS X Mavericks or later, add a status menu to make it easier to mirror your displays. Use this menu to select an Apple TV or television to use as a display. It appears when you connect to an HDTV, or when an Apple TV is available on your network. To add the menu to the top of your screen, select "Show mirroring options in the menu bar when available."
The blue boxes represent all displays that you've connected. The white bar at the top of both boxes represents your primary display. In video mirroring, both displays have a white bar because they show the same information.
You might see black bars on the sides of the screen image. This happens if you choose a resolution in the Display pane that only one of your displays supports. Your Mac uses the closest matching resolution.
To switch between video mirroring and an extended desktop, press Command–Brightness Down.