Go to Starbucks, Barnes and Noble, coffee shop, or somewhere that has a wifi hotspot so you can register the device. You will only need to do that one time and for it to download any books you have purchased. I don't know if you are referring to a Kindle Fire or one of the others. The KF can be sideloaded with books from your PC with a micro-to-USB cable. Not sure about the other versions.
AMR