The G string 7th fret, D string 12th fret and the B string 3rd fret are all the same note. They sound the same to me. THey are all D's. I'm pretty sure thats right. I guess they are different 'voicings'. My teacher is showing me different voicings of chords. Different chord positions but they all sound the same sound. But you could play either of the different D's I guess. Anyways, on the sheet music I got it has a chord name above, like Gm6. How are you supposed to figure out what a Gm6 is? Or do you just have to memorize all these chords... like D#7#9 and E11 stuff like taht.