Explanation

Box 1: Azure Active Directory
Create the company users in the Azure Active Directory.
Box 2: Power Apps admin center
In the Power Apps Admin center, manage environments that you've created and those for which you have been added to the Environment Admin or System Administrator role. From the admin center, you can perform these administrative actions:
Create environments.
Rename environments.
Add or remove a user or group from either the Environment Admin or Environment Maker role.
Etc.
Reference:
https://docs.microsoft.com/en-us/power-platform/admin/environments-administration
https://docs.microsoft.com/en-us/dynamics365/marketing/dynamics-365-admin-center
https://powerapps.microsoft.com/sv-se/blog/introducing-admin-center-for-powerapps/