To get to the administration interface, you will need to browse to https://portal.microsoftonline.com and log in with the credentials you chose during the sign-up process in Chapter 1, Getting Started:
The first step of utilizing Office 365 for your business requires that you add your domain (for example, yourcompany.com) in the portal. This is a necessary place to start as your
domain will be used later in many aspects of the Admin Portal. To add your domain to Office 365, click on the Domains menu option on the left (see the following screenshot):
You will see that the tenant domain already exists (for example, yourcompany.onmicrosoft.com) in the listing. This domain cannot be removed, however after completing the next few steps, your Office 365 subscription will be set up
in a way that the tenant domain will not be seen by your users.