Getting in
Bandzen is in a closed beta. You cannot sign up on your own — an account exists because someone sent you an invitation.
If you have an invitation
The invitation email carries a link. Follow it, create your account, and you land on setting up.
Your account is the email the invitation was sent to. If you sign in later with a different email, that is a different account with none of your work in it.
If you do not
The sign-up screen has a No invitation? form. Leave your email and it joins the waitlist. That is the whole mechanism: the list records that you asked, and invitations go out from it as places open up.
What the waitlist is not
Joining it does not create an account, hold a place, or start a trial. Nothing happens until an invitation arrives.
Signing in later
Bandzen and the content CMS share one sign-in. That matters in one direction: if you have also been given a teacher role, the same account reaches both. It does not work the other way — being a candidate gives you nothing in the CMS, and opening it signed in as a candidate shows a page telling you so. See Getting access if that is what you were expecting.