There are a huge amount of apps to help recognise what we have… Each of these sites also gives a huge amount of information about how we can help preserve biodiversity.
Nabu is a great place to start for recognising birds and other common organisms. http://www.nabu.de
If you are interested in plants, then pl@ntnet is a good introductory app for identifying plants. You can get it and lots of similar ones at Google Play.
When you feel more confident, Naturgucker is a huge German wide database relying on community science to record organisms https://naturgucker.de/naturgucker.html
Places to visit
If you prefer to be onsite, then the Botanical Gardens in Dahlem is great place to start. The botanical museum and botanical school will certainly keep you occupied… https://www.bgbm.org/
The Natural History museum is another fount of information… It often has lectures and exhibitions about sustainability. https://www.museumfuernaturkunde.berlin/