Google Home can now play your stored or purchased music on Play Music

The feature gives priority to uploaded or purchased content over tracks on the radio station, when you ask Google Assistant to play you a given song, album or artist. However, subscription on-demand songs would be chosen before your stored tracks, unless you specifically asked Google to play a given track from your library – “Google, play X from my library”, for example.
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If Play Music is not set as the default player on your Google Home, you’d need to explicitly ask it to play the track on Google Play Music – something along the lines of “Play X on Google Play Music” – if you want to listen to on-demand or uploaded tracks.
The feature is currently rolling out across regions around the globe and should soon be live in the countries, where Google Home is supported.
source: Google