Writers of science fiction and fantasy actually build worlds.

Authors of science fiction and fantasy literally build worlds.They make rules, maps, lineages,languages, cultures, universes, alternate universes within universes, and from those worlds sprout story, after story, after story. When it's done well, readers can understand fictional worlds and their rules just as well as the characters that live in them do and sometimes, just as well or even better than the reader understands the world outside of the book.But how?