Several folks at AQ have self pubbed Kindle edition ebooks at Amazon.com via the KDP (Kindle Desktop Publishing) program. Depending on how they price their books, they can earn either a 35% or a 70% royalty for each book Amazon sells. For this reason, Kindle ebook authors tend to scatter links to their books all over the Internet. Stands to reason. If readers don't know about your book, they're not likely to buy it.
Authors who enroll in the free Amazon Associates program https://affiliate-program.amazon.com/ can earn an additional 4% if someone buys their ebook after clicking the authors link to get to the ebook's Amazon page. There are some additional rules you can research yourself at the Amazon Associates site. For example, I think there's a time limit after clicking during which the reader\buyer must buy. Amazon makes it easy to create a link with your unique associate ID. Just type in an ASIN for your ebook or other product and then you can copy and paste a link (with or without a graphic) that links to Amazon and tells them you sent the buyer to them.
From what I've seen, Amazon Associates can even earn a 4% commission on a sale even if the person who followed the associate's link buys a different product. I made 26¢ when somebody purchased a book that I never even heard of. No, I'm not getting rich off of this. I had only one link out there in a web site that nobody but foreign hackers visited. Recently, though, I decided to give it a try and populated my web site FalafelJones.net with a few links that I thought fit in with my books.
There's a caveat though. Certain web sites, such as Wordpress.com will immediately and abruptly suspend your website if "affiliate" or "click through" links appear on your web site.