Multiple displays
>>> If you use a MacBook, or work with several apps that you always prefer to see in detail, it's possible you may benefit from using multiple displays.
Connect one to your Mac and System Preferences’ Displays pane gains an Arrange tab. Drag the blue rectangles that represent your displays to their relative physical locations. Drag the menu bar to the one you think of as your primary one. If external displays aren’t detected, hold Opt and click on Detect Displays.
‘Show mirroring options…’ adds an AirPlay icon to the menu bar. you can use that to choose an Apple TV and specify whether it should mirror3 what’s shown on your Mac, or work like a separate display, complete with corresponding desktop and windows.