An outline, is basically a mini version of your book to be. It can be anywhere from a couple of pages, to forty or so. Many authors create an outline before they begin writing their book. This is one way to avoid suffering from the dreaded (writers block). Essentially, the book is already done. All the author has to do is flesh it out from the original outline. So...should "you" create one before you start your book? I suppose that depends.
As I mentioned, creating an outline can help a new writer avoid writer's block. Because the entire story has already been written in compact form, all he or she has to do is fill in all the detail. Another advantage to making an outline is that the author is able to write much faster. (More words per sitting) Because they already know the path the characters are going walk, there isn't a whole lot of (what should I have them do next) involved. Remember, the story is already complete and just needs to be told.
So why doesn't every author make an outline before they write? Well, for some of us this method just doesn't work very well. (That's correct. I don't use them at all) Why you ask? It's because I just can't think that far ahead. If I had the ability to visualize a complete story from beginning to end, I might use this technique. The truth is, I don't know what's going to happen until it happens. I change things on the fly. When I first start writing, I have very little idea of where any of this is going.
I once watched an interview with one of my favorite authors, R A Salvatore. He was talking about how the business works from being traditionally published author. He HAS to write an outline, then give it to his bosses in order to get the green light to go ahead and write the book. He talked about how they would look it over, give him the OK, then hand it back to him. When leaving, he would get as far as the secretaries office before throwing it right in the trash. All he needed was the OK to go ahead with the project, and now he has it.
I feel the same way. I can't handcuff the characters and force them down a premeditated path. By the time I start writing the book, everything I put in the outline will be void anyway. An outline doesn't matter to me because as the story progresses, I'm going to change nearly everything as I go.
So am I saying don't use an outline? No. I'm saying it can work very well for some authors, yet prove to be a terrible hindrance for others. Experiment, and see which kind of author you are. Find out which way works best for you.