There are different ways to achieve this. You could put all the music files in a restricted folder then when someone wants dl a song you could move it temperarly to a public folder. You could store their users session ID or a randomly created hash to a que. This hash/ ID would be the name of the file to download. the dowloads would have a time to live.
You can not say you know how to do something, until you can teach it to someone else.