The director of a musical guides the actors in playing their parts, oversees the details of the show's design and works to create a piece of theater that fulfills the vision of all involved.
The music director conducts the orchestra, if one is used, and rehearses with the actors to help them learn the music in the show.
What's a musical without dancing? A choreographer is the person who creates the dance steps in a musical. They also help the actors find their characters' physicality.
Light, set, and costumes designers bring the visual elements of a musical to life. They work with the director to help bring his vision to stage.
Stage managers keep things running smoothly, both during rehearsals and while the show is in production. They file rehearsal reports to keep all involved abreast of any changes or developments in the process. During the run of the show, they often are responsible for calling the light and sound cues, supervising the run crew and making sure the actors know when it is time to go on stage.
The crew is responsible for running the light and sound boards, operating the fly system and supervising the wardrobe.