As Kyle has stated he doesn't use any Amazon plugins, but if you do choose to use one here is how you get your Amazon secret access key and Amazon access key ID.
You shouldn't need these keys if you are just using Amazon Associates program without using a 3rd party plugin like Easy Azon, WooZone, Amazon Link, etc. Only for an Amazon plugin that requires that you use a secret access key or and ID.
It's a pretty straight forward process.
Make sure you DO NOT use AWS Amazon. This is NOT tied to your Amazon Associates account.
Once, you have signed up you will be able to get the required information that you need.
It's important that you have the required information otherwise there is no way to tie it to your Amazon Associates account. Meaning, you won't get credit for commissions.
Please let me know if you have any questions down below.