You can sell your e-books through Online e-book retailers or through your own website. Some popular e-book sellers are:
iTunes:
Apply to the iTunes book’s account program. The service only accepts the epub format (and multi-touch). ISBN is recommended but not required for any book you are offering on the iBooks Store. An ISBN uniquely identifies the book and its current edition and helps you to ensure that you are marketing the right book. The ISBN is also required for reporting your book’s sales to industry reporting agencies and charting organizations.
Amazon Kindle
Amazon accepts epub format, independently publish with Kindle Direct Publishing to reach millions of readers. Get to market fast. Publishing takes less than 5 minutes and your book appears on Kindle stores worldwide within 24-48 hours. Make more money. Earn up to 70% royalty on sales to customers in the US, Canada, UK, Germany, India, France, Italy, Spain, Japan, Brazil, Mexico, Australia and more. Enroll in KDP Select and earn more money through Kindle Unlimited and the Kindle Owners’ Lending Library.Keep control. Keep control of your rights and set your own list prices. Make changes to your books at any time.
Google Books
Promote your books on Google—for free. Apply to the partner program. Submit the epub and pdf version (up to 250MB file size). No ISBN required, google will assign one after upload.
Nook (Barnes and Noble)
Publish your book on the popular NOOK eReader and your book will share virtual shelf space with the latest New York Times’ bestsellers, Pulitzer Prize winners, and time-honored classics.
Sell From Your Website
You can always sell your PDF ebook from your own website. There are many different free e-commerce programs you can use to set up your own online store.
Which will mean you will no longer be splitting the profits with ebook vendors. Another positive of selling from your own site though is that you can set up your own affiliate program. This means that you can offer a commission to Internet users who are will to help you sell your book.
While this still means you will be splitting the profit once again, it also means that you’ll have the opportunity to recruit hundreds of people interest in helping you to sell your book on commission. Which in turn, can result in you selling countless copies that you wouldn’t have otherwise sold.
The downside about selling the books on your own is you’re vulnerable to pirating. And it means you may not have access to the large audience that you would have through the large ebook vendors.