[Tracy McCabe]

I downloaded music from a music app from the play sore, but it is not available on my music library.

[Rukbat]

Restart the phone (or run media.Re.Scan) to rebuild the media database. Then open the music app and look for the music. (Downloading doesn't trigger a rebuild of the database.)

[Mooncatt]

Which app did you use to download the music? Some apps save them in such a way that only that specific app has access to it. That way they can help prevent copyright violations. If you downloaded a regular audio file like an mp3, that should show up in the music app automatically.