Offline playback is available only on mobile apps. (Users on desktop and web apps play downloads when offline).
The operative step for offline playback is to first cache (selected) music in device memory (when the app is online).
The steps to cache music for offline playback are as follows:
a) login on the mobile app and select album (for offline playback)
b) click "+" to add "New Playlist", name the Playlist and click "OK"
c) manage the playlist's tracks (delete individual tracks or keep all tracks or reorder), keep "Offline Playback" active and click "Save Changes" and "Yes" to "Update Playlist?"
d) Wait for "Done" notification
e) Once notification is reported, the app will start to cache the playlist in device memory.
Music caching is done in the background. If there are multiple playlists set up for offline playback, the app will queue the process.
You can check the status of caching progress by going to My Music>>Playlists and open the new playlist:
Caching status is denoted by a "download" icon beside each track. A track in cache memory is marked by the icon in Yellow.
Once caching is complete, the music will be accessible (for up to 30 days) to playback when offline.
Next section: "Audio Interface Settings".