Purchase iPhone in Germany as a tourist and tax return questions

Hi, I will be travelling to Germany and I have some questions and hope you guys could help if you know?

1. my trip will be one month.
2. what is the tax return %% if I purchase an iPhone there.
3. can I straight away use the phone coz I plan to get it on the first day I arrive there. From my experience in Japan they will automatically deduct the amount right at the Apple Store. Not sure how it work in Germany Apple Store?