Most of the e-book downloads are delivered through BookFunnel.com. They make it easy for readers to get e-books onto their device, no matter what e-reader is used. They have great customer support and are there to help if you have a problem getting your book onto your device. Android, iPad, iPhone, iPod, Kindle, Kobo, Nook, or computer are all supported.
Here are Amazon’s instructions https://www.amazon.com/gp/sendtokindle/
From your browser
Send news articles, blogs posts and other web content to read them anytime, everywhere on Kindle devices or reading apps.
From your desktop
Send your personal and business documents to read them anytime, everywhere on Kindle devices and reading apps.
From your e-mail
Attach and send your documents to Kindle using the “Send-to-Kindle E-mail Address” to read them anytime, everywhere on Kindle devices and reading apps.
From your Android device
Send documents from your Android phone or tablet to read anytime, everywhere on your Kindle devices and reading apps.