levi
Still fresh, damnit!
According to wikipedia it should have the notes of the C major chord repeated by blowing through to holes, and have all the missing notes from the major scale when you suck. And like you say pushing the key/lever in raises everything by a semitone, making it d-flat major. The main use for that in pop music in c major is that you can start out a semitone above the note and bend down to the right note using the button I think, but I'm no harmonica player.