You manage Office 365 using the O365 Admin Panel or Admin “App”. When you login unsing an administrative account you will find an App called Admin.
You can could also click on the nine dots on the upper left hand side of the startpage and select the app.
When you start the app you will find a navigation bar on the left hand screen that is currently set to home. To better understand the structure of the menu and the handeling of users you have to think of how the licensing model works.
On the users section you can generate user logins. Licenses get booked and bound to the users account, that defines what apps the user can use. User get sorted into groups, that defines what resources and privileges the user can access inside of an app.
The onboarding of a new user looks like this:
Cheers, Ori