There are 6 levels or episodes, each of which is split into two elements: wandering around the town where the Jonas' live, completing tasks and the like, before ending with you completing a guitar-based rhythm-action mini-game. All of the songs are new for the game and once you've unlocked them, you'll be able play them on request.
As with the Guitar Hero games, the rhythm-action part works as notes drop down the DS screen onto your guitar, spread across four columns. What you have to do is select the correct column using the D-pad - there's one column for each direction, up, down, left and right. Then with your stylus, you have to strum on the guitar's string area when the falling note passes through.