A casting director is someone who helps pick the actors for a movie, TV show, or play. They work with the director and producer to find the best actors for each role in the story.
First, they read the script to understand the characters and what kind of person would fit each role. Then they look for actors who have the right look and skills to bring the characters to life. They might hold auditions where actors come and perform scenes from the script, and the casting director and other people involved in the production watch and decide who is the best fit.
Once the actors are chosen, the casting director works with their agents (like a manager who helps find them jobs) to negotiate their contracts and makes sure they are ready to go when filming or rehearsals begin. Basically, the casting director helps build the team of actors who will tell the story in the best way possible!