Most music players want you to think in tracks. Audionix thinks in folders, which is how a lot of people already keep their music: one folder per album, one for a ripped mixtape, one for the artist you can't stop playing.
The whole setup
Open the REAR tab and add a folder under Source folders. Audionix scans it, and each album folder inside becomes its own cassette. Go back to Library, insert one, and it plays.
Add a parent folder such as Music and you get the whole shelf in one go. Add a single album folder and you get one tape. You can add more than one source folder, and you can come back to the same panel whenever you want to change what's in the pile.
Two other layouts work too. A folder that holds album folders instead of songs is treated as an artist folder: each album inside becomes a tape, and the artist folder's name goes on it as the artist. And any loose songs sitting directly in a source folder gather on a tape called Singles.
What the tape tells you
Each cassette carries a title, an artist and a tape length. The artist comes from the tags in your files. If no single artist shows up on at least half the tracks, the tape reads Various Artists, which is usually the honest answer for a compilation. If you'd rather name it yourself, a name you set by hand always wins.
The tape type is picked from the files too: lossy formats get one kind of tape, higher-resolution files get fancier ones. The tape types article has the full rundown.
Your audio files stay on your phone. Audionix reads them from the folders you pick, and it can't see anything outside those folders.
If your folders are a mess, that's fine for a start, but a little tidying pays off quickly. We wrote down how to organize them so the shelf looks the way you'd expect.