The page states "There are 3 Steps to validate your application":

1. Brand Registration – submits your customer profile and A2P messaging profile together to the campaign registry. Only after it is APPROVED can you do step 2.
2. Campaign Use Case – registers what kind of messages you send. Only after it is VERIFIED can you do step 3.
3. Adding SMS Numbers To The Messaging Service – attaches your purchased number(s) so they can be used for composing.

Tabs for steps 2 and 3 only appear once the previous step has reached the required status. You cannot open this page until your SMS account is connected and your profile and trust bundle are at least in review — otherwise you are redirected back to the profile page.