How do I get books on my Kindle without wifi?

I just bought a wifi only Kindle, connected it to my computer using the usb, and tried to drag and drop books that I bought using Kindle for PC to the “documents” folder. But when I tried to read the books on the Kindle, it said that they weren’t registered to my Amazon account, and couldn’t be read. I can’t get a wifi connection in this house. I really want to start reading. How do I solve this problem?

Kindles come with a USB cable. Instructions for transfering files via USB can be found here:

http://www.amazon.com/gp/help/customer/display.html?nodeId=200505520&#usb

How To Connect Wirelessly on a Kindle