Your site administrator is created when you first set up your SharePoint site. However, you will likely have a number of users that will be collaborating using the SharePoint site. Follow the below instructions to add your additional users within the Customer Control Panel.
1) Log in to your Customer Control Panel and select the subscription containing your SharePoint hosting from the drop-down menu at the top, right-hand side of the page.
2) Navigate to the SharePoint tab, then to the Users sub-tab, and click on Add New User.
3) Next, select whether the user is an Existing Service User or New Service User. In this case we are making a new user.
4) Enter the credentials for your new user and click Next.
5) Now you need to select the role for your new user, and enter their email address for the notification email.
6) On the next screen, check the parameters carefully for your user, and click Finish to finish creating the new user.
When the user has been created, an email will be sent to the address you entered and the user will be able to log in to SharePoint.
Your newly created user will now appear in the list of service users.
You should repeat this process to create accounts for all of the users who will need access to your SharePoint site.
Each user you create will receive a notification email containing their login credentials. They will now be able to login and modify the site as per the role you set for them upon creating their account. See more information in this article about managing your SharePoint users.