Cast your screen from your Android device


Connect your Android device to the same Wi-Fi network as your Chromecast device.


Open the Google Home app Google Home app.



In the top left corner of the app's Home screen, tap Menu Menu >  Cast Screen / audio.



Click the "Cast Screen / audio" then Select your Chromecast device.





Cast your screen from your Apple device


Google Home Mirror is not available to for iPhone yet, to Mirror an iPhone you'll need to download a third party app.


The recommended app to use is MomoCast

https://itunes.apple.com/in/app/momocast/id931719129


After installing, Open Safari on your Apple Device, and press the open with icon 



Scroll to the More tile,



The press the 3 dots.



Enable 'Cast with MomoCast' in Safari


Once enabled press  again,



Then press  Cast with MomoCast.