Applicants who have acquired an international qualification to attend university and aim for a PhD apply directly at the Studierendensekretariat (Student's Office) of Bielefeld University.
You will receive information about your application from Bielefeld University. In case you fulfill all of the requirements, you'll get an admission from Bielefeld University. You can use this admission to apply for a visa at the embassy. After your arrival in Bielefeld, please go to the students' office (Studierendensekretariat) to enroll yourself.
There are no deadlines for an individual doctorate. You can apply, be accepted, and enroll as a doctoral student at any time. Research Training Groups and Graduate Schools generally have set application deadlines. Go to their homepages for further information.