The "cast" of a play or movie is the group of actors in it. A "star" is a famous or important actor. "Studded" can mean covered with small protruding bumps. A piece of clothing is "studded with jewels" if it has lots and lots of them, covering it like a crust, and not just one or two. "Star-studded" means "covered with stars, twinkling with stars, bright with lots of stars." Usually, a movie has one or two stars, and a few "supporting roles" played by good actors who are not quite stars. A "star-studded cast" means that the movie cast, instead of just having one or two stars, had many stars in it. For example, the 1956 movie "Around the World in Eighty Days" (La vuelta al mundo en ochenta días) had more than forty stars in it.