If you purchase a Kindle through your Amazon account, the Kindle is automatically associated with that particular account. If you receive it as a gift or through another source, you need to log in to your Amazon account and manually register your Kindle. Once your Kindle is registered, you can purchase Kindle books through your Amazon account or the Kindle itself, as well as sync your Kindle books through several different devices. Your Kindle will always automatically log you in to the associated Amazon account.
Go to Amazon.com and log in to your Amazon account.
Click "Your Account."
Click "Manage Your Kindle."
Click "Register a Kindle."
Go to your Kindle. Press "Home" and "Menu." Choose "Settings." Copy the 16-digit serial number from the Kindle's screen to the registration page on your computer. Click "Register" to associate your Kindle with your Amazon account.
Go back to your Kindle. Once the serial number is associated with your Amazon account, your Kindle should automatically log in to the associated Amazon account. If you are uncertain that your Kindle has automatically logged in to your Amazon account after it's been registered, press the "Menu" button. Choose "Shop in Kindle Store." The Kindle store will launch and allow you to shop using your Amazon account settings.