To sync a device to your Amazon.com account, first download the Amazon Appstore or Kindle Reader on that device. When opening the app for the first time, you're prompted to sign in to your Amazon account. Once this step has been completed, the device is automatically added to your Amazon account. Devices can also be managed by going to My Account on the Amazon.com home page, scrolling down to Digital Content, and clicking Manage My Content and Devices.
Once Manage My Content and Devices loads, a menu with several options appears at the top. Clicking on the Devices tab displays a list of devices registered to an account. From here, it is possible to de-register devices, set a device as the default and find out details about the registered devices.
To register a Kindle, tap the Menu icon on the Kindle and select Settings. Once you have reached the Settings option, select Registration. You can then select which Amazon account to link to your Kindle. If you do not already have an Amazon.com account, the screen prompts you to create one. A registered Amazon.com account allows you to transfer books and content across devices and to purchase books and apps.