Hi from a fellow German,
I am pretty new to all those things myself, but I learned quite a bit so far.
I'd recoment to sign up with
www.fertilityfriend.com. It's free and easy to use. Every morning, you meassure your body temperature and check your cervical fluid type. You add this data to their charts and then it shows you over the course of your cycle when you're fertile. This is usually 2 days before and on the day of the ovulation, if I recall right. I think FF is pretty nice and helpful. You will learn to understand a lot about your cycle
You could also use an
Ovulation Predictor Kits (OPK). I have no experience with that, but I am sure someone else on those boards does
Hope that helped you at least a little bit.