Definitely take this all with a grain of salt—I am by no means a legal expert, this is just my advice.

Privacy Policy

Required by law in Germany if you are collecting any sort of data about your users (even if it is being collected by a third party through your app, or if it is entirely anonymous data).

Data Processing Agreement

Required by law in Germany for the same reasons as the Privacy Policy. This agreement makes it clear how your users’ data is used.

Cookie Policy

Required by law in Germany if your application uses cookies of any kind (mostly applies to web app and web technologies)

Terms of Service

Highly recommended. This may protect you immensely if and when you end up in a legal situation down the road.

Other

Otherwise, you should look into these as well if applicable:

• EULA (if distributing your app to be run on someone else’s device)
• DCMA Policy (if you host and share any user-generated content)
• Return Policy (if you are selling anything)

These documents matter most if (1) there is money involved or (2) when you are receiving, processing, storing, or sharing user-submitted content or any data about your users. This is because you are less likely to end up in a legal mess if you’re not taking people’s money or data.

Starting out, you can find templates for these online. A template will be better than nothing at all. Then, if you are able down the road, you can hire a legal professional to write and review your documents for you. A legal professional might recommend more specific documents or different versions of the same document as well.

Not sure about Germany, but in the United States it’s fairly inexpensive to start an LLC. You can then put legal documents under that new entity instead of your own personal name. This can protect you and your own belongings from any unfortunate financial or legal situations.

Again, if you’re not receiving money or any user data, you don’t have to worry quite as much. However, it never hurts to play it safe. Mistakes happen and anyone can get sued.