If you want to register your Kindle reading app with Amazon, you have to choose because there are four process with different devices. With iOS, for Android, PC and for Mac.

Now I am going to explain the Android registration procedure below:

• First you need to open your Kindle for android then click on Start Reading.
  
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• Now you'll be asked for enter the account info after fill the information click on Sign in.
  
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Above process is Android. If you want to register with different device follow the steps provided on Amazon Kindle fire support.

You may enroll your Amazon Kindle fire tablet computer with Amazon.com from the preferences portion of one's program. Click on your tablet previously mentioned and click Obtaining began or you may visit Amazon Kindle Support for device-specific incremental directions.