When I try to register using the course search, nothing happens.
Registration using the course search is reserved for diplom- and magister students.
Should you still be able to register this way, it is most likely that the connection to your examination regulation (Prüfungsordnung) hasn't been made. If you register this way, your registration will only half-work; you may not be able to sign up for an examination or your study performance may not be saved correctly.
If you are a Bachelor's or Master's student, you should not register using the course search! Always register in your personal registration area in TUCaN (Courses -> Registration).