I hope to have answer for my quetion.
I will move to live in Berlin with my husband. I have a Tunisian driving license so i need to know:
How and where can I exchange my license?
What are the essential documents I have to prepare?
The procedure is explained on this page (in German). You don't need many documents: basically some ID, proof of residence in Berlin (you will have that after the mandatory registration), a passport photo, your current driving license (and a copy), possibly a translation.
The main difficulty is that unfortunately for you, Tunisia is not on the list of countries whose driving licenses can easily be exchanged in Germany. You will need to retake the theoretical and practical exam to get a German license (you will however be exempted from the mandatory training, you can go to the exam directly if you want to). If you don't speak German, you can also take the exam in English, French and a few other European languages.
You will also need a test of your vision and a proof that you took a special first-aid course (it takes several hours but it's quite cheap something like €15-30 plus about €6 for the vision test).
Having gone through the procedure myself, I can say that the official page linked by Gala is not very accurate.
I wrote a detailed post about what the procedure really is.