The formal requirements for establishing a business or the establishment of a branch are listed by the authorities' guide of the Federal Ministry of Economics (Bundeswirtschaftsministerium - BMWi).
It provides information on the required applications and the concerned authorities. It also provides addresses, directions, opening times and contact details. In this way, you can also apply directly to the authorities if you do not want to avail the service of the Point of Single Contact.
For the authorities' guide of BMWi, please visit: www.bmwi-wegweiser.de (This link leads to a range of information that is only available in German)