A narrative tells a story. Telling a story aloud is very different from writing a story down on paper. When a story is told out loud, we tend to "hop around", leave out important details, and forget to explain characters. In a sense all of that is okay, our gestures, expressions, and tones of voice can carry a lot of information. The reader of a written narrative expects more and needs more. The story cannot be simply "talk written down.
All of the important events and details must be organized, clear, and descriptive. A fully developed narrative story involves a main idea, which is introduced in the beginning, more detailed and eventful in the middle, and wraps up in the end.