Let’s assume that you have a book written and you wonder with whom or how you can publish it. Also, if there are many choices, which might you consider in what order?
Fiction is the easiest. Don’t self-publish it if you want it printed in paperback or cloth; bookstores and libraries won’t buy it from you! So here you must go to a larger or major publisher, submit the novel (some chapters with a synopsis and cover letter), and get them to agree to lovingly put your book in print.
But you can publish it as an ebook yourself, actually about seven times simultaneously. Prep the book like you want it to appear and convert the text into digital book format (takes an hour or two). Then submit it to ancillary publishers (like Kindle, Nook, Smashwords, Apple, Lulu, etc.) and let them publish it for you quickly and free! My book (bound or from the same ancillary houses) called How to Get Your Book Published Free in Minutes and Marketed Worldwide in Days walks you step-by-step through the process. (Many do this first while they are waiting for the big house rejections.)
Nonfiction books are easier to publish or get published.
Here, both standard publishing and self-publishing work well, though the latter requires you to do the marketing too. (The best of all nonfiction worlds is to produce a niche book, pretest it, and sell it almost risk free and quickly to your niche market. You usually print niche books or products by  in the next paragraph.)
If you want yours to appear in bound format (paperback, sometimes in cloth), (1) you can have it done by a major house, (2) you can self-publish it (in larger quantities by a short-run printer) or more one-by-one in POD (print-on-demand)—or do both simultaneously, and/or (3) you can have it produced quickly by Create/Space [which can be your POD producer] or Blurb.
If you want your nonfiction book published as an ebook (it can also be a paperback or cloth at the same time), again go to the ancillary publishers and let them release it, one-by-one or whenever you get it submitted: Kindle, Nook, Smashwords (Sony), and Lulu.
I suppose there are some deviations and combinations too, but the paths and order suggested above might get you headed the right way. (I expand on every point here in many other blogs written in the past three years. Just move backward to find what you want in the list to the right at http://blog.gordonburgett.com.)