There is a difference between print on demand (POD) and printing companies. It's important to know this before deciding how you want to get your book into print. After reading this page, compare the facts to those presented on my printers page.
     Not all POD companies are the same. The first type will charge a set fee per title. Most of the ones I've seen have packages ranging from $500 -$4000+. Each package will give you more options which include how your book is sold, how many free copies you receive, and the amount of editing and such the service provides. On the up side, these services will allow you to upload a plain Word document or other file and then assign a representative to do all of the required formatting which will put the text into book form. The downside, of course, is that you'll have to sell more copies before you make a profit. Another drawback is that, although the service will get your book posted at places like Amazon.com, they won't do anything to market (advertising, etc) the book unless you pay additional fees.
     You don't have that much cash laying around? There are other PODs which, believe it or not, are completely free to use. The main drawback is that you have to know or learn enough about various types of software so that you can do all of the formatting yourself; however, most of these services provide the basic instructions about the proper size of margins and other things you need. Once you have your files uploaded, you do have to buy one book, known as the "proof copy". This is sent to you so you'll see exactly how your book will look. The "free" services may also have a small fee attached to each title if you choose to have them place your book on a list for possible distribution to book stores, libraries, and multiple online booksellers.
     Just because your book is listed at one of the larger online bookstores that doesn't mean you'll ever sell a book. Don't sit back and hope someone will stumble across the listing. Get out there on the street, talk to people, and find ways to advertise. The POD will act as your publisher, but the marketing is up to you. The best part of using a POD is the fact you don't have to order a minimum number of your own books. They have the ability to print as few as one book or as many as ... well, as many as you need. As a person orders a book, the POD prints the required number of copies and mails them directly to the customer.
     Important: Never sign on with a company if they insist that you sign over the copyright of your work to them.