Remember all the research you did in school when you had to write a paper or create a new project? Hours spent writing out your notes because we couldn’t highlight encyclopedias and we had to avoid plagiarizing like the plague. Ugh, tedious, boring work just so we could get a good grade.
Guess what? If you want to become a published author those years were not in vain! And whether your story takes place on another world, in another country, or in another time you must do your research BEFORE you put ink to paper or fingers to keys. Your story must be based on facts, accuracy, and attention to detail; otherwise your reader may do their own research and, if what you say is not true then you will lose credibility and likely a reader.