Although Amazon works with a wide variety of industries now, it originated in books. And it still dominates the book industry. The Wall Street Journal recently wrote about how Amazon “commands an unrivaled customer base for the books, e-books and audiobooks it publishes.”
Part of what helped Amazon with ebooks is KDP, the platform where indie authors can upload and sell their books on Amazon. KDP, like most platforms these days, makes the process easy, though you’ll still want to take some time to figure out your ebook pricing. You can even sell PDFs on Amazon (and the other major retailers).
KDP offers some perks for authors who enroll in KDP Select, in exchange for selling their books exclusively with Amazon. In the past, that’s worked out really well for some authors. However, as the platform grew, it’s gotten more competitive. And there have been articles about people cheating the system.
Nowadays, people tend to advise indie authors to “go wide”, meaning, publish on as many platforms as possible. With that in mind, you may want to consider using IngramSpark or another service to sell print on demands books, instead of Amazon. Or you can even use both.
You many also want to look into marketing more with other major retailers, such as Barnes & Noble. Barnes & Noble now offers print on demand, where you can print books for personal use or sell your books on their platform. Barnes & Noble also allows authors to advertise on their website, similar to Amazon’s ads. (The Book Designer has a good breakdown of how to sell ads on B&N, and the difference between B&N and Amazon ads.)
And if you’re feeling really ambitious, you can try to get your book placed in Barnes & Noble and other stores. Nonfiction Authors Association has a breakdown of what that takes, including having a strong cover and ISBN and having a pitch packet (cover letter, marketing info about your platform, and other materials that may impress book buyers). There’s also an option to work with book distributors, but be sure to follow their submission guidelines.