Teacher user accounts have the ability to create new users. This is primarily used to create accounts for students so the students do not have to go through the account registration form. 

You will see the Add user button on your home page if you have been assigned the Fair Teacher role once your have logged in. You are assigned the Fair Teacher role by a website administrator after your credentials have been confirmed.

Each new user must have a unqiue user name and email. You should fill in as much detail as possible. The new user will receive a confirmation email. They will then be able to log in. You will only be able to log into that account if you have the user name and password. In general, teachers should not be logging into these accounts. This process is simply to make account creation easier. 

If you only need to create the fair submissions for students and will be entering all their information then you can simply create multiple submissions using your account. 

Teachers should check out the Manage Schools documentation to see how to manage submissions for their school by users with their own account. That ability allows a teacher to view, but not modifiy, the submissions of their students.