For Instant Articles to be enabled they need to go through a review process to ensure they conform to Facebook standards. In order to submit your articles for review you need to generate a minimum of 5 articles on your production feed. All your articles need to have styles attached.
It takes 2 business days for Facebook to review your Instant Articles feed. If approved you'll be able to put your articles live. If rejected you'll need to fix any errors highlighted and re-submit.
Read more about the review process on the official Facebook Instant Articles documentation