You can use the Google Home app to group speakers for synchronous music throughout your home.
Make sure that your mobile phone is connected to the same Wi-Fi network as your speakers.
To group speakers:
1. Open the Google Home app .
2. Tap Add > Create speaker group.
3. Tap each device you want to include in the group.
4. Enter a name for the group.
5. Tap Save.
You can learn more about using Chromecast built-in at support.google.com/chromecast.