Registry at the consulate in Frankfurt: for your first inscription you must go to the consulate. You will find the documents provided on the Internet or by calling them.
Cards: When you want to work more than 3 months, you must have a specific visa (Aufenhaltserlaubnis). You must go to the office for foreigners (Ausländerbehörde) with:
Come with an International citizen form (your own town hall will indicate you how to get it).
You will then get the form EG-Ausländer that you and your company have to complete. Then bring it back to the above office or send it by mail.
You should get your authorisation card within the following 2-3 weeks.