EPUB (electronic publication) is the global standard, open-format file type for digital books, allowing text and images to “reflow” and adapt to any screen size, from phones to e-readers. It packages web content (HTML, CSS, etc.) into a single, zip-compressed file, making it highly flexible, accessible for print-impaired readers, and supported by most devices (Apple Books, Kobo, Nook) except native Kindles, which need conversion

You can read EPUB books with any EPUB reader, that includes Amazon Kindle. To upload your book to your Kindle, use

https://www.amazon.com/sendtokindle

The file will be available as soon as you sync your library.

NOTE: For whatever reasons, uploaded books will NOT show up in Kindle Web.