The power bank comes with a short Micro-USB cable that’s about 12 inches long. It’s the same type of cord as your Kindle Fire’s charging cord.
To charge your Kindle Fire, you may use either the short cord or your usual Kindle Fire charging cord. Insert the small tip of the cord into your Kindle Fire as you’d normally do. Then, plug the other tip, which is the big USB end, into the USB port on the battery pack where there is an engraving “OUT.” Charging should begin automatically. You may want to check the battery level of the power bank before charging the Kindle Fire.