What that basically means is that your story must have a beginning, middle, and an end. Again, that may sound simple, but most writers do not develop these segments well. The beginning for example deals with the introduction of the characters, their personalities, and their dilemmas. This is when the tone of the book is set. The beginning of your book, usually the first two chapters, are your first opportunity to get the readers attention.
Most people have very short attention spans.
They will likely sit the book down never to pick it up again. But beware, many authors come off too harshly with profanity and heavy dialogue in an effort to get out to a fast start. That may get the readers attention, but it can also take away from your opportunity to set the tone and paint a vivid picture of the story. The middle of the story is generally used to create tension, the conflict . This is where so many good books flop because the author fails to make the readers care about the characters dilemma.