The primary location to manage user accounts and services is the Microsoft Online Serivce Administrator Center.
https://admin.microsoftonline.com/
Often this may be managed by your Microsoft Partner (ie: Web-Kong). Each Microsoft Online Services account will initially have one administrator assigned to their account. Additional administrators may be assigned if necessary. The administrator account has the ability to create user accounts and assign licenses to them. They may also manage storage assigned to user accounts.
In addition the administrator may create SharePoint portals and/or assign accounts with this privilege.