Travellers coming from a country outside the European Union (EU) can benefit from duty free shopping outside the airport. They get back the value added tax that is usually included in the normal price.
Look out for the tax free sign when you go shopping or point it out to the sales assistant at the cash point. You will receive a form that you have to fill in.
When leaving Germany you have to present the goods you bought to customs. You will receive a stamp on the above mentioned form. Now you will be able to claim back the value added tax, it will be payed directly in your credit card account.
At airports and in big cities you also will find refund points where you can hand in your refund form and receive direct payment of the value added tax. The following link gives an overview of refund points and further information on tax free shopping in Germany: http://www.taxfreeworldwide.com/en/are-you-shopper/10-0.html