Often I see a science fiction or fantasy story that starts like this: a handful of paragraphs of description that slowly start to explain how the world works, and who the characters are. The problem is that there is no problem.
See instead the following example:
Matt’s foot hurt, and it was getting worse. He knew that if he told anyone, they might leave him behind.
Now, you don’t know how old Matt is, or if he’s white or brown, living in contemporary New Jersey or on a distant alien planet in the far future. You don’t know whether he’s human or alien. You don’t know who he’s with or what he’s doing or why. But in a sense, none of that matters. You’ve probably imagined that he is on a hike or a hunt or a trial of some kind, maybe military training, maybe a punishment. More importantly, you know that he has a reason for doing what he is doing, because he wouldn’t do something this uncomfortable without a reason. So even though you don’t know what that reason is, you’re probably eager to find out. You know he’s in trouble, and you want to know if he can solve his problems.
The point is, a reader doesn’t have to understand that much about the world in order to sympathize with the character. All we need to do is get hooked on an interesting person with an interesting problem. This is the go-juice that keeps readers interested — we want to know what happens next.
Often new writers think, “I need to take my time and introduce the characters!” But a novel or short story isn’t a cocktail party, where social niceties require people to be polite and pay attention. It’s very common that the writer needs to write their way into the world, especially the kind of complicated worlds that exist in science fiction, fantasy, and horror. The writer might need to figure out how the gravity works and the government and the basic geography and technology and the tensions between the characters and the character motivations and whose story it is. This is fabulous work for the writer to do, but it is not the same thing as telling a story. A science fiction or fantasy story in its purest sense is a person with a problem that he or she is grappling with. And a novel is what happens when the problem is bigger and longer and more complicated.
The basic rule here is “show, don’t tell.” This is classic writing advice that may be easy to misunderstand. As a reader I don’t want to see the whole world. It’s too much to care about. I want to feel like I have a sense of the whole world, but I’ll get that through the plot and the depth of the characters.
So don’t worry so much about the reader understanding everything about how the world works. Tell us a story.