In order to Add a New User to your account, you will firstly need to select your Office 365 subscription from the drop down menu if you haven' already.
Click the Microsoft Office 365 Button at the top of the screen.
Then you will need to select the tab 'Users'.
This will bring you on to the page where you can view, manage and add users. To add a user select the 'Add New User' button.
This takes you to the user configuration screen where you can enter the user details and set up a suitable email address for the user.
Once you have filled these details out, the next step is to assign the user an available licence in the second second. In this example I had a Business Essentials licence available which I selected.
You have now successfully added the user and can proceed with logging in to the Microsoft Office 365 control panel: https://portal.office.com