Make sure your Mac and TV are on the same Wi-Fi network
Turn on your TV and enable AirPlay if it supports it
On your Mac, click the Control Center icon in the menu bar
Click Screen Mirroring
Select your TV from the list
Enter the AirPlay code if prompted
To stop sharing, click Screen Mirroring again and choose Stop Mirroring
If your TV does not support AirPlay, connect a compatible Apple TV or use an HDMI cable with the proper adapter