Casting the device screen means that on the TV a copy of what you have on your device will appear on the TV screen. Make sure that both your phone and your TV are on the same Wireless network. Install the Google Home app, in it you will find the option to cast the device screen. Important: Not all devices are able to correctly cast their screen as this requires quite a bit of resources on the part of the device. A pop-up warning you that your device is not optimized for casting will appear when trying do cast your device screen.