Sign up at Amazon.com for an author's account, which allows you to publish your books as Kindle editions (see Resources). Amazon provides an author's dashboard that lets you upload and proof your books. Authors maintain control over book pricing. The dashboard also allows you to keep track of sales and royalties, which Amazon is responsible for paying out on a regular schedule. Authors can remove any book uploaded as a Kindle edition at any time, and there are no limits to the number of books you can sell.
Take advantage of Amazon's print-on-demand publishing service to publish your Kindle editions in paperback (see Resources). There is a charge for print-on-demand with Amazon, but the increased potential for exposure and sales makes it a viable way to sell a Kindle book to a wider audience.
If you have a personal website, use it to advertise and direct visitors to your Kindle editions. While Amazon reaches a large audience, especially where Kindle users are concerned, there are numerous ways to expand that audience and increase Kindle book sales. Amazon doesn't own the rights to your work, nor do they prevent you from publishing your book in other formats. You are free to offer your book in other formats and with other publishers, which allows you to take advantage of alternative audiences while you make use of the Amazon platform.