The form on the principal tab is for an free Principal account.
You looking to sign up as a student?
Just go to the CozyUni site at which you want to sign up as Student and click the Sign up link near the top of the page.
A Principal account allows you to create a CozyUni site. Please use a valid email address, cause a email with a link to activate your account will be send to this email address. Problems? Add a post on the Support forum.