I have read all kinds of books on plotting, structure, and story. All have different methods for completing a story. Some start with outlining while others start with character development, while others tell you to skip both. Yet all have the same basic structure designs.
No matter how you write your story, it must have a beginning, a middle, and an end. I should note that there are those that say that method is old and out dated; however, no matter what they wish to call their elements, all stories start somewhere, end somewhere, and along the way there is a middle of the tale. Without them, you have nothing.
Your beginning does not have to start at "the beginning." It could start in the middle of an event, say a bank robbery or an awards ceremony. It could even start before the beginning, say at the birth of the protagonist, even though the story takes place at the end of his life. No matter where your story starts, it has a beginning, and it tells us who, what, when, and where. This is where we get to know the score. It is the set up to the story. In short, your have to start somewhere and you have to make us care enough about this particular tale to keep up paying attention.
Likewise, all stories must have an ending. If your story simply ends with no conclusion, you will leave your audience dissatisfied. Happy or sad, your audience needs to know it is indeed the end of the tale. Consider this, if I said I got up and went to work, you can honestly say, "who cares!" You would want to know, what happened at work, what problems did I encounter, and how did I solve those problems. In your story, your ending is how your protagonist solved his problems or how he was overcome by his problems. An ending to a story is simply a conclusion, not when you choose to stop telling your story.
That leaves us with the middle. This is more than just the place between the beginning and the end. This is the heart of the story, the meat and potatoes. This is where many a story falls apart. This is where we need a little planning. I will say that, unlike the blueprints for a building, one can deviate from the outline, especially when you are inspired by an idea. However, that would require you to have a plan in the first place, and having a plan to deviate from will help your story from wandering away from you.
Now it should be understood that that this is the most basic of story structure. There are many other elements that go into a story. There are those we all know, and there are those that we may not be aware of, but that is for another day. For now, let us remember that the beginning is the set up, the end is the conclusion, and the middle is our story.