Hi,
It will be better if you contact potential supervisors first and ask them whether they would be interested to work with you and whether you can study in English. There is no application process to the universities as it is in GB or USA. You are normally not considered a student anymore but a researcher. There a some exceptions where you find courses comparable to GB. However, you normally will be employed by the university (if you are lucky and they have the money). There is some good information on the website of the DAAD.