You need to be part of Amazons Associates program in order to start getting commissions. The reason we wait until now is that you need a website in order for Amazon to attract you into their affiliate system.
If you have set up your website in accordance with this guide you will be accepted. Once accepted your first job will be to add your special Amazon tracking links to your product pages created in Step 5.
The video below walks through how to sign up to the Amazons Associate program.