Something fictional has been invented, most likely for a book, play, or movie. But if you're really self-centered, you might think a fictional story is actually about you.
As the adjective form of fiction, fictional covers all the creative fabrications that arise out of a person's imagination, which might then enter a novel, a screenplay, or some other form of storytelling. While fictional characters may be based loosely on real-life people, they never actually existed. In the movie "Citizen Kane," Orson Welles transformed the real newspaper mogul William Randolph Hearst into the fictional Charles Foster Kane. Hearst never went around whispering "Rosebud."