Write your book. The book can be on any topic or any genre that you'd like. The word or page count isn't important, because an ebook can be created with as little as 10 pages. It's best to convert the file to PDF because it will be easier to convert into an ebook, however, .doc or .rtf will work as well.
Upload your book file to an online self-publishing website such as Lulu.com. There are a wide range of self-publishers out there, but Lulu.com is completely free and will give you the option to keep your manuscript as an ebook only. Once your file is uploaded, Lulu.com will give you the option to add a cover design, your name or any other information that you want to include with your ebook. They have preset cover designs that will make the process run smoothly.
Set your price. You can adjust your price to any number that you'd like, but remember to keep it reasonable so people will purchase your book. Depending on the page count of your ebook the price could range from $5 to $25.
View your completed ebook to make sure it is set to your standards. Lulu.com will give you the option to "Edit" your book, so if you notice anything you'd like to change you have the ability.
Promote your ebook by emailing the link to your book on Lulu.com or by posting it to social networking sites like Facebook. You have now created an ebook for free and one that has potential to generate some income.