An outliner sits at their computer or with pen and paper and plan their story. They may spend a day or two writing an outline or several months. The outliner may write a couple of sentences for each chapter, then they start to write the story. Then you have the heavy outliner. This person plans out each chapter, and scene before they write start on their book. They include their hook — their opening sentence. They plan out each chapter and scene, making notes about their main character, the antagonist, and the minor characters. The heavy outliner leaves nothing to chance, covering the beginning, middle, and end of their book. If they did research for certain elements of their story, they include that as well. Outlining in this manner keeps the writer on track with their story. Rarely do they hit snags in their plot or confusion in their time line. The characters and antagonists behave themselves as well.
If you are the type who loves details, you could spend as much time writing your outline as you do the actual book. There’s nothing wrong with that, since you are building a solid skeleton of your story. When you sit down to write it, you begin to flesh out the bones, giving it a solid form, and most importantly — a voice. In order to have less editing once the first draft is finished, outlining the story will help in this. Another thing to consider, an outline can also be used to create a chapter by chapter synopsis. You have the information for each chapter, all you need to do is flesh it out a bit. Remember, the details you put in the outline are up to you. There is no set method or form.