Because in Campus Management your study progress is registered and documented, it is necessary to register for your courses for the specific semester during the registration period formally. Because this registration is formally also the legally valid course registration, the registration is mandatory before doing anything for the course (like taking the exam).

But don't worry, during the period you can register and de-register your course as you wish on your own if you want to change something or don't want to take the course anymore. But also: there are some courses which are restricted in the number of participants. If you want to take one of those, You should register within the first phase of the period because after that you can only take those with capacity left. 

The whole registration period lasts one month and is divided into two periods. Period one ends on the Friday before the lecture period starts at noon with distributing the spaces to those who registered. Phase two ends at the end of the second week of lectures and is for making changes regarding the course registration. As soon as period two ends, the registrations are fixed.

For the registrations itself you log in in Campus Management (either directly or via your My.FU-portal) with your FU-account. You can find your courses under "An-/Abmeldung"(registration/de-registration). If it is a new course, in the bottom left corner is a button saying "Neues Modul auswählen" (choose new course). Then there is a list with all courses which you can register for. Choose those you want to take. Because most of our courses have two parts (lecture/exam and exercise/tutorial) you usually have to register for two parts to do a complete registration. To register you click on the box, save it and confirm it. And that is all, with that you are registered for the exam (if you register for the lecture) and the tutorial part. The specific tutorial group is then later chosen in the learning management system. 

This video shows you more precisely how Campus Management works and also explains more how the registration works. You can find here a reference guide.