there is a music symbol i`m not famliar with and i know that someone online has to know what it is and what it means. its this tr symbol. i`ve seen it on a couple of pieces by mozart and all i know is that more notes are played then what is shown in that measure. can anyone tell me what it is?

In music tr stands for "trill". A trill is going VERY quickly back and forth from the note the tr is next to to the note right above it. (A full step above, not the next chromatic step, excluding natural half steps.) Good luck!

trill - back and forth between the note written to the next note in the scale or the next note as denoted by previous sharps/flats/naturals in the bar, lasts for the full count of that note.