You have to have a Kindle or the free reading app to give the book a place to go before you can download it. The free reading app is avaiable for Android phone or tablet, iPad, iPhone, Mac, Windows 8 PC or tablet, BlackBerry, or Windows Phone.
Download the app here, except now the book isn't free anymore. The app still is, and I would download it to your PC anyway because there are tons of books that are free, especially classics and "how-to" type books.
Yes. This. Plus Amazon has daily specials on all kinds of books for free as promotional give aways. Once you get your kindle app just do a search on "free books" and see what is on offer that day.