A production designer is like someone who arranges all the toys in your room to make it look just how you want it to.
When a movie is being made, the production designer is in charge of making sure everything looks just right. They work with the director and other people on the movie team to figure out what the setting should look like, and then they create a plan for how to make it happen.
Just like you might put together a puzzle, the production designer puts together all the pieces needed to create the setting for the movie. They might decide what colors to use, how the furniture should be arranged, and even what kind of flowers should be in the background.
The production designer doesn't just work behind the scenes though. They also help the actors understand the setting they are in and may even help create props for them to use.
Overall, the production designer is like a big toy organizer - they make sure everything is in its place and looks good so everyone can enjoy the movie!