How does the magic actually work?

Hi all, I am a musician and experienced web developer, and whenever people ask me how all those AI sites acually work under the hood, I am embarrassed to confess that I don't have a clue.

Who knows a bit more about what exactly happens when you send off a prompt?

How are Music AI sites trained? Do you feed them music all day? And how is the music then analyzed and separated into rhythm, melody, style, instruments and vocals?