well a pull of is the partner top the hammer on. they both are used to get the smooth legato sound.
right pull ofs are used to go smoothly from one note to a lower one on the same string. eg 7 to 5
often notated as 7p5
first place your first finger on the 5th fret then the third finger on the seventh. pluck the string. now you want to take your third finger of the seventh fret, but you dont just lift it. you have to dragf it down slightly (or up), this should make note freted on the fith fret ring out. remember hold the fith fret down constantly.
this can be done between any two fingers.
hope this is clear enough.