While holding the buttons first (depending on controller setup) you then press the arrows, in that order, to play the guitar. Think of a real guitar, you hold down a chord shape (button like A,B,X,Y for Xbox Controller Setup) and then strum in a direction or pluck strings in a certain flow of direction (Arrow Keys). That was the idea, however I noticed you can soft press a button and then an arrow without having to keep holding down the button.