https://en.wikipedia.org/wiki/Kindle_Direct_Publishing

Kindle Direct Publishing is Amazon.com's e-book self-publishing platform launched in November 2007, concurrently with the first Amazon Kindle device. Amazon launched Kindle Direct Publishing (KDP), originally called Digital Text Platform, for authors and publishers to independently publish their books directly to the Kindle Store.

Authors can upload documents in several formats for delivery via KDP website and charge between $0.99 and $200.00 for their works. These documents may be written in 44 languages.

In 2016, Amazon also added a paperback option, which uses print-on-demand technology with the goal of offering digital and print to self-publishers. Amazon has been promoting to its authors the capability of publishing both e-books and paperbacks through the same platform.