Ok, here is how to do it. I have the Kindle fire and get as many fee books as I can handle and not from amazon all the time. I use Guetemberg and some other place. If they are free, they will download to your download folder on your hard drive. Then you can open your Calibre and if the books are not a mobi file, calibre will convert them for you to ebup for ipad and mobi for kindle. Calibre will make a folder on your hard drive for the books it converts and all you have to do is hook up your kindle and transfer them to your documents in Kindle.
Now if they are asking you for information, I wouldn't download. Unless of course you are getting it from Amazon, that is ok. Amazon will treat it like a purchase and it will be zero on your account.