To learn how to enable Google Cast in your Connected Audio speaker, please see this article: How do I enable Google Cast on my Connected Audio speaker?

Google Cast is a streaming protocol from Google that allows you to easily stream content from e.g. your mobile device to a Google Cast-compatible device. ​

1	Start playing music Simply open your favourite music app and start playing content Locate the Cast icon
2	Select your speaker Select the speaker you wish to cast to in the list Your Cast-compatible device will now start streaming directly from the cloud, and your phone will only act as a remote control.

It is also possible to create speaker groups and stream to multiple Google Cast speakers simultaneous. To learn how to create Google Cast speaker groups, please see this article How do I use Google Cast for multiroom?