An application is required if a course of studies or subject is restricted in admission. In the case of admission-free study programmes, direct enrolment without prior application can take place within the specified period. You can find out here whether a course of studies or subject is restricted in admission.
Where and how you apply for a place depends on several factors, among others of your citizenship, the country in which you obtained your higher education entrance qualification, as well as the course of studies for which you wish to apply.
If you are a citizen of a non-EU/EEA country and have a German Certificate, you should apply to the Registration/Admissions Office.