The verb expatiate means "to add details to in order to clear up." If your story is confusing to everyone who hears it, certain key parts must be missing. Better expatiate so that people can understand it.
To pronounce expatiate correctly, accent the second syllable: "ex-PAY-she-ate." When you expatiate on a piece of writing, you add details. The goal is to make your ideas clearer to readers, perhaps by offering an example to help them understand. Teachers can tell when you are expatiating and when you are just adding to what you've written, say, to reach a certain length requirement. That's usually called "padding."