AirPlay mirroring lets you share what’s on your Apple device — websites, presentations, spreadsheets — with everyone in the room on a bigger screen. Beforehand, devices you want content mirrored onto must be compatible with AirPlay and connected to the same network as your Mac. Devices compatible with AirPlay include; Apple TV, (some) Smart TVs, and any other systems that run AirPlay.
How to Mirror
Open Control Center in the menu bar
Click Screen Mirroring
Next, there will be a list of devices that your Mac detected in the same network
Click the desired device(s) to begin mirroring
Whichever devices are currently mirroring will display a blue icon, signifying they're active
To stop mirroring, simply re-click the active device(s)
To control the layout of Screen Mirroring, open System Preferences > Displays > AirPlay Display Menu.