This app gives you video (youtube) walkthroughs to all the test chambers in Portal 2 (Singleplay and Coop!).

If you hang at a level, just start the app on your phone an watch in parallel how to solve the test chamber :)

NOTE: For many of the higher levels and the Coop levels there are only longer running videos with multiple levels in it available. I'll try to update the app as soon as per-level videos become available :)

Screenshots: