To use the Extramaterial, everyone must now have their own account with their own login. It is free and relatively easy to create an account, you can do it here. If you already have an account at Natur & Kultur, login as usual at nok.se/login.
If you are a teacher (remember to connect your account to a school so you get teacher permission) you can also create accounts for your students. You can do that from the User (Användare) menu when you are logged in to your account. If the students don’t have an e-mail address, you can still create accounts without it.
As a teacher it helps if all the students have their own account, so you can follow their progress when doing exercises. It also makes it easier for the students to save their work until the next time they login to their account.