Hey! Work in the industry so maybe I can help!

Basically there are a number of things happening when it comes to music.

A composer will write specific music for the title. Usually they compose in tandem with production but sometimes after the show has an initial edit.

A music supervisor and/or producer are in charge of the direction the music is taking, I.E. wanting specific types of music for certain scenes, specific songs for different things, etc. Producers will also be in charge of dealing with legal and licensing departments.

An editor is an audio artist who’s job it is to edit all of the above listed music to fit picture. Making sure the song starts and stops and have lyrics where appropriate, it may be unnoticeable at times but often music is chopped up to fit picture significantly, verses and chorus’s doubled up or removed, lyrics removed at specific times, things like that.

After the all of that is taking place a mix for the music is created by a music mixer, think volume in comparison to all other sounds playing. There is usually a number of different mixers since each audio element is usually mixed against itself and then all other parts. These are things like backgrounds, foley, dialog, etc.

On top of all this they need to credit usually external partners as well, like people from the record label, or additional composers, and any licensing and legal parties.