This system uses central computer science accounts. All students in computer science or related subjects should already have an account. Your username likely starts with s9 or s8.
If you lost or don't know your password, use https://sam.sic.saarland/accounts/password/reset/
To change your password, go to https://udo.cs.uni-saarland.de/pw/chgpwd.php
If you are certain that you don't have a computer science account, contact the department's system administrator Alexander Fauß. Do the same if you want to offer a seminar.