One of the many reasons people read is to experience unfamiliar places, people, and events. Books (both fiction and non) are written about space travel, aristocracies, Regency balls, cults, dreamland, Mexico, and sports figures. Authors must sufficiently describe these things so that readers who know nothing about space, inherited titles, or dancing in Empire gowns are able to imagine them.
We don’t want to confuse or alienate readers by not explaining things with which they are likely to be unfamiliar. Nor do we want to interrupt our stories or talk down to our readers by overexplaining.
Finding that balance—a story that sweeps readers along into new, exciting, and imaginable territory—requires a sense of your audience. If you are writing a mystery novel that will likely be read by mystery aficionados, it is not necessary to explain what dusting for fingerprints is. If you are writing a mystery novel that features a person being murdered in a grain silo, it is probably necessary to describe the silo rather than assume that all of your readers have seen the inside of one (unless your novel is for a niche audience of mystery-reading farmers).