The easiest way to start is by launching your social shopping website as described in the tutorial, and then using that URL to apply for an affiliate code from Amazon.

You can use your regular Amazon account for this, but to obtain affiliate codes, visit:

US: https://affiliate-program.amazon.com
Canada: https://associates.amazon.ca

The application process is straightforward and, most importantly, instant. It literally took me just 3 minutes to get my codes.