You may have heard about Kindle Unlimited but you might not know what it is. This page should clarify the basics. This is an unofficial explanation by indie author Stuart J. Whitmore. If the "nutshell" explanation is not enough, scroll down to the short Q&A section.
Definitely not. You can use your computer and/or mobile device to read Kindle books. Just install the free Kindle app that Amazon provides for your device or operating system. You can even read a Kindle book in your Web browser; watch this short video for a visual demonstration.
No, the "unlimited" refers to how many you can read, rather than the number of books available. Whether a book is available in Kindle Unlimited depends on the publisher. For indie writers who self-publish, including a book in Kindle Unlimited means the book can't be available on other e-book platforms like Kobo, NOOK, Google Play, etc. That exclusivity requirement discourages some authors from including their books in Kindle Unlimited. If a book is not enrolled in the program, you won't be able to read it through the Kindle Unlimited service. (Often, however, you can buy it on the Kindle platofrm for a relatively low price, especially if it is from an indie author.)
Actually, when you read a book through Kindle Unlimited, the author will get paid. Instead of you paying the author, Amazon does. The payment is variable and the author won't know what it is until later, which does deter some writers who prefer to know what they will earn. Also, the amount that is paid depends a lot on the text in the book, so the program is not as attractive to authors of picture books and other materials that have more images than text.
Sometimes, but not all of them, and not all of the time. He believes it is important to give readers a choice in where they do business, but he also acknowledges that many people already use the Kindle for all of their e-reading and would like to have as many books as possible to choose from in Kindle Unlimited. If there was no exclusivity requirement, he would probably leave his books enrolled all the time.