An authorization key (also known as an Auth Key or merely as Key) is assigned to each license whether it is a trial account or a purchased plan.
Main Auth Key: It is auto-generated and comes filled in. This key is unique.
Regenerate Auth Key: Clicking on the Regenerate Auth Key button replaces the existing key with a new one in the box.
Documentation: Clicking on the Documentation link takes you to the API (Application Program Interface) documentation. It will be useful to you if you want to understand the technical and development side of the software.