In a case of emergency, please always dial the emergency number 110!
Police work in Germany is basically the responsibility of the federal states. You can therefore report a crime directly to the police station in your area. The police officers will take your statement on the spot, answer your questions and take any available documents. Your criminal complaint will then be examined and possibly forwarded. If necessary, the Federal Criminal Police Office will be involved by the responsible authorities (state criminal investigation offices / public prosecutor's offices).
In some cases it is possible to file a report via an online police station, for example in cases of theft, fraud or damage to property.