It is an underappreciated truth that world-building applies to all fiction. World-building is usually associated with science fiction and fantasy, where a writer is telling a story in an imagined world which obviously works differently from our own everyday reality. For example, a fantasy author might need to decide how long an adult dragon can typically fly before needing to land and rest. A science fiction writer might timeline how commercial space travel results in the colonisation of the moon by various companies over several decades. These are the sort of things we often think of when we hear the term world-building. An author will imagine the cultures, the peoples, the history, the politics, the flora and fauna, the laws, the science, the technology, the magic, whatever else it may be that is relevant, in order to establish the way the world works in the story they wish to tell.
Which means that if your novel is set in everyday reality you might think world-building isn’t something to concern you. But pause for a moment and think on this—all fiction is a subset of fantasy, in that all fiction is a work of the imagination. Authors don’t just invent characters (including their pasts, hopes, dreams, crimes and so much more). They create the fictional places in which they live, work, fall in love, and on occasion, even commit murder.