To use it, you can enable display mirroring from the shortcut or settings menus. Your device will need to support Miracast, which has largely fallen out of use and was actually dropped by Google with Android 9 Pie. That's because there aren't likely too many use case scenarios (such as a lack of internet connection on your device) that don't let you use an app to watch programs. Miracast is still largely available on Windows devices, however.