What is "Amazon AWS Access Key ID" and "Amazon AWS Secret Access Key"?
To get access to Amazon affiliate products database you need to sign up for Amazon Associates program and to Amazon Product Advertising API.
The Product Advertising API provides programmatic access to Amazon’s products selection and discovery functionality so that you can advertise Amazon products to monetize your website. When you sign up for Product Advertising API you obtain Access Key and Secret Key. They are used to personalize your Amazon database search. You use these keys in Amazon Feeds tool at RSS Ground.
Amazon also provides you with Access and Secret keys when you sign up for Amazon Web Service. But you still need to sign up for Product Advertising API to be able to search Amazon products. And if you have your keys both in AWS and in Product Advertising API, you should use those from Product Advertising API.
Please see user tutorial on how to sign up for Amazon services and obtain Amazon keys.