You can manage Office 365 from the "Office 365" section on the "left hand" navigation or the "main screen"
Q Login to Office 365
You can log into your Office 365 Account by clicking "Login Here" and entering the username and password
If you have updated your username and password it will not be replicated here
Q Use A Domain with your Office 365 Account
Click "Change DNS to use your domain with Office 365"