This information is not relevant if you do assignments through a direct link.
To sign in, go to https://pro.quarterfall.com. You are asked to provide your email address. Next a mail is sent to you that contains a link that you can use to login and that brings you to your dashboard.
You cannot register as a student yourself. Instead, your school or teacher will invite you by email. Follow the link in the email and you will be asked for your name. After this you can sign in using your email. If you did not get an email, contact your teacher.
If you are a student at multiple organization (departments, institutes), you can change the organization in the avatar menu at the top-right to see the corresponding courses.
In the past you might have had a password for Quarterfall. Quarterfall no longer uses passwords but now uses the magic link mechanism described above. So you will never need that password anymore and can discard it.