The connection from the computer or iPad to Apple TV is called AirPlay. The AirPlay icon is a rectangle with a triangle at the bottom. This icon appears on the right side of the Mac Menu bar.
You can also use AirPlay to mirror or extend everything on your Mac display. The display must be connected and awake.
1. Click the AirPlay icon AirPlay icon in the menu bar, then choose your Apple TV under "Connect To AirPlay Display." The icon turns blue when your Mac is using an AirPlay display.
2. From the same AirPlay menu, choose either Extended Desktop or one of the mirroring options under "Use AirPlay Display To."
To stop using your Apple TV as an AirPlay display, choose Disconnect AirPlay Display from the AirPlay menu. Or just press the Menu button on the Apple TV remote.