heh, wuts a Tremolo? And How do you play one? and wut if there are like a whole bunch of them, like right by eachother?

Tremelos on the violin are played by quickly rubbing the bow backwards and forwards against the string. It gives it a very dramatic sounding effect.

On the piano, you play a tremelo by quickly alternating from one note/chord to the other note/chord, which is indicated by several lines between the two.

Violin - place your bow on the string... and RIP! @_@ well, play very quickly, using very short bow-lengths, which creates a unique effect

Piano - place your fingers on the tremolo notes and SPAM! =_= nyeh, playing those notes really quick, kind of like as if you were playing a trill... extended..