Depending on the size of your organization, you may want to designate several admins who serve different functions. The following admin roles are available:
Global admin: Has access to all administrative features. Global admins are the only admins who can assign other admin roles. You can have more than one global admin in your organization. The person who signs up to purchase Office 365 becomes a global admin.
NOTE Make sure all users who are global admins in your organization have a mobile phone number and alternate email address in their contact info. Check out Change your organization's address, technical contact email, and other information for more details.
Billing administrator: Makes purchases, manages subscriptions, manages support tickets, and monitors service health.
NOTE If you didn’t purchase Office 365 from Microsoft, you can’t make billing changes and therefore can’t be assigned the billing admin role. For billing issues, contact the admin at the organization where you purchased your subscription.
Password administrator: Resets passwords, manages service requests, and monitors service health. Password admins are limited to resetting passwords for users.
Service administrator: Manages service requests and monitors service health.
NOTE Before global admins can assign the service admin role to a user, they first assign the user administrative permissions to a service, such as Exchange Online, and then assign the service admin role to the user in Office 365.
User management administrator: Resets passwords, monitors service health, and manages user accounts, user groups, and service requests. The user management admin can’t delete a global admin, create other admin roles, or reset passwords for billing, global, and service admins.
Exchange administrator: Has administrative access to Exchange Online through the Exchange admin center (EAC), and can perform almost any task in Exchange Online.
SharePoint administrator: Has administrative access to SharePoint Online through the SharePoint Online admin center, and can perform almost any task in SharePoint Online.
Skype for Business administrator: Has administrative access to Skype for Business through the Skype for Business admin center, and can perform almost any task in Skype for Business Online.