In order to transfer data from your computer to your Kindle you will need a Kindle USB cable. Plug the larger end of the cable in the USB port of your PC and the other end in your Kindle device. Next, right-click on the file you want to transfer, select Copy and open the Kindle drive from My Computer/Computer. Double-click the Documents folder, and paste the copied files. Also, you can use the drag and drop function. After that, go to System Tray and safely eject the the Kindle device. For further details, you can check the official Support page.