Apple TV how to download apps
There are two different German TV apps as far as I can see.
They are both available to download for free.

As for the Apple ID and iTunes account confusion; maybe this will help. I've taken a photo of my Apple ID for you:





Now I've censored the beginning of the email addresses, but you can see that I have more than one account associated with my Apple ID; one for iCloud, one for iTunes, and one for Game Centre. 

Most people probably use the same account for everything. And you probably do too. So when it asks for your iTunes password, it's probably the exact same one that you've already provided.

Also; your iTunes account is not just for downloading music. It's also for downloading apps, movies &amp; TV shows, and more (like virtual books and podcasts).

I hope this helps, and if you have any follow up questions, feel free to ask.