Is there any German course that I could do on my Android device? Whether it's an app or an optimized web site it's fine by me.
I'm using Anki flashcards. There is also version for Android.
Anki is a program which makes remembering things easy. Because it is a lot more efficient than traditional study methods, you can either greatly decrease your time spent studying, or greatly increase the amount you learn.
You can download German dictionary and start learning :-)