A set designer is responsible for creating the fictional world of a play, movie or TV show. Consider, for example, the long-running sitcom Seinfeld. Set designers were responsible for designing everything in the main setting — Jerry’s apartment — from the furniture to the fridge magnets. They also created the show’s secondary settings, such as the coffee shop and comedy club.
Set designers work on scenery and details. In this field, “scenery” is defined as anything that is used as a fixed backdrop (e.g., furniture and wallpaper). They may also work with set dressing, such as decorations and furniture.
Note that set designers don’t just create indoor spaces for actors. They also work on outdoor scenes. Set designers are responsible for both the smallest details of a scene, as well as the “big-picture” items.