Just the basics: If you're a self-publisher, it means that you're the publisher. All that means--and it's a lot--is that you own all the publishing rights to your book and you're in charge of everything.
If you're a self-publisher, it doesn't mean you are a vain, ego-driven crummy writer. It doesn't mean your book isn't good enough to be published by a "real publisher." It doesn't mean you are supposed to do your own editing, book design, page makeup, and printing. It doesn't mean you would be any good at those things if you tried. You just have to do them yourself--or find somebody to do them for you. At your direction.
Being a self-publisher is a little like building your own house. You could do everything yourself, but you'd have to be able to do your own architectural design, materials buying, excavation, masonry, framing, roofing, plumbing, electrical, HVAC, and finish carpentry. And you'd need tons of time. On the other hand, you could farm out some of the jobs. You might even hire a general contractor to do most of the coordinating work yourself. But you're still in charge. You should be overseeing what the house looks like, what kind of materials its made of, and how good the workmanship is. Because you're paying the bills, and it's your house.
That's what it means to be a self-publisher. The Publishing Pro.