Hey @hp  they're just chord inversions and the letter after the slash will be the lowest sounding (BASS) note of the chord.  You can use them to make a chord easier to finger depending on where you are on the neck or add color to make a progression more interesting or easier to play.  A whole lot more than that but in a nutshell thats it.  Ahem..cough   as an addition little known fact they were invented by Saul Hudson...  Jotd