Do you know how to do "Through Fire and Flames" on Expert Difficulty in Guitar Hero 3? Then this will be a piece of cake for you. For the rest of us, it might take a couple of tries to unlock this. In Strum you play a banjo, and to advance you have to repeat the notes the banjo plays. There are four strings on the instrument, where each string represents one of the four main Xbox 360 buttons.
Pro tip: Each button represent a unique tone, so if you manage to put a tone to each button, you will have a much easier task at hands.