I am a relatively new guitar player (about a year and a half), and I am getting a lot of the basic chords down pretty good now.  I have started to really expand my song list, and I read a lot of tab  - I keep coming across chords that look like combinations, or two chords, such as A/D.  There are several other combinations similar to this, and they show the little six string graphic with how you play the chord.  I cannot figure this out!  First of all, A/D doesnt look like either A or D, and it doesnt sound like a "conventional A or D either.  Am I supposed to change my fingering to transition from A to D?  This chord is shown with  the B and E strings fingered on the secong fret.  You dont play the E or A, and the D and G are open.  What am I supposed to be doing here, and, how do I read these graphics on other combinations??