Login at SuperAccount Control Panel with the main account's username and password.
Click on the Website Link.
Click on the Email link.
Click on Manage mailboxes.
Select your domain name.
At the next page, there is a Add New Mailbox section.
Before the @ sign you type in the name of the email account you want to create.
Type in the password, click on Add.
You've completed creating a new email account for your domain.