Downloads, offline playback, and using your phone as the source
Downloaded music plays with no server and no internet, and can still feed a network streamer.
Downloading saves the actual audio to the device, at any level: a track, an album, a playlist, or a weekly mix. Offline copies play automatically whenever your server is unreachable. There is no "offline mode" to remember to switch on.
Settings → Downloads shows everything you have saved, split by albums, tracks and playlists, with the space used. A live queue shows what is in progress, waiting or failed, and lets you retry only what failed. A storage limit caps how much space downloads may use and survives a reinstall.
The part people do not expect: when you are away from home and your server is unreachable, your phone can become the source for a network streamer. A downloaded album can play on any UPnP system anywhere: at a friend's house, in a hotel with a UPnP soundbar, not just through your headphones.
Still stuck
Write to us with your server, your streamer and what you expected to happen. If you can, send the diagnostic log from Settings, it usually answers the question faster than a description can.