When your users see the "Login with Amazon" button on your website, they'll know that they can log into your website without needing to manually enter some of their personal information.
That's because "Login with Amazon" allows developers to get information from Amazon user profiles such as names, email addresses and zipcodes:
Login with Amazon allows users to login to registered third party websites or apps ('clients') using their Amazon user name and password. Clients may ask the user to share some personal information from their Amazon profile, including name, email address, and zip code.
Facebook and Twitter are already providing this via their APIs. Those are the famous Sign-in with Facebook or Sign-in with Twitter buttons:
Amazon released an introductory video, titled "Meet Login with Amazon":
The Privacy Notice URL field in the Register Your Application section, inside the account dashboard, is defined as:
The "Privacy Notice URL" field is mandatory to be filled. It applies regardless of how you register your application:
The "Login with Amazon" feature makes it easier for developers to allow Amazon users to quickly register or log in on developers' websites or mobile apps.
The same URL found on your website should be added in the Privacy Notice URL field in Amazon's Application Registration Information form.