Use multiple displays with your Mac
You may be able to connect more than one display to your Mac. To do so, you need a video cable for each display, and you might need an adapter. See the Apple Support article Adapters for the Thunderbolt 3 or USB-C port on your Mac or iPad Pro.
After you connect the displays to your Mac, you can choose whether to use them as an extended desktop or for video mirroring.
Connect the displays
For each display, securely connect a video cable (and adapter, if necessary) from a video output port on your Mac to the video input port on the display. See About the video ports on Mac.
If your Mac has Thunderbolt ports , you can connect up to two displays. If the displays themselves have Thunderbolt ports, you can connect one display to another, and then connect one of the displays to a Thunderbolt port on your Mac. If your Mac has two Thunderbolt ports, you can connect each display to separate Thunderbolt ports on your Mac.
If your Mac doesn’t detect a connected display
Set up the displays as an extended desktop
You can arrange your displays in any configuration to create an extended desktop. For example, you can set your displays side by side to create one large continuous desktop.
On your Mac, choose Apple menu > System Preferences, click Displays, then click Arrangement.
Follow the onscreen instructions.
Set up the displays for video mirroring
Video mirroring shows the entire desktop on each connected display.
On your Mac, choose Apple menu > System Preferences, click Displays, then click Display.
Set both displays to the same resolution.
Click Arrangement, then select Mirror Displays.
Set up some displays for mirroring and others for an extended desktop
If more than two displays are connected to your Mac, you can specify that some displays use mirroring, showing the entire desktop, and other displays show the extended desktop (displaying the desktop across two or more displays). For example, if you have three displays, you can have two displays showing the same information and the third display showing the extended desktop.
Use the task above to set up all the displays as an extended desktop.
Press and hold the Option key and drag one display icon onto another display icon to mirror those two displays.
If you are playing a DVD on a television connected to your Mac, click the Arrangement button in Displays preferences and move the menu bar to the television. If you don’t see an Arrangement button, your Mac is only capable of mirroring.