It is very easy. Once you have signed up, just download the app, open it and answer the questions of the setup wizard and you are good to go.
No, it is not possible (yet) to make international calls with the Freedom app. You can only make calls to German land line phone numbers and mobile phone numbers.
The audio quality is exactly the same as the audio quality of your mobile phone. The app uses ‘call through’ to set up the phone calls, so you won’t notice any difference in the audio quality between a regular phone call with your mobile phone and a Freedom app phone call.
The app uses the network of your mobile phone provider, so if you have bad connection in a certain area, it has to do with the quality of the reception of your cellular provider.
Yes, it works exactly the same as with your mobile phone calls. You don’t need to change any settings.