Thank you all for your help

Hi, This is my fist time playing a MMO type game, and in this game I am a sith marauder. Could anyone give me some tips, tactics or stratigies on how to be an effective part of the group. so I don't mess up in Heroics or flashpoints. What does a DPS class do in a group fight? I messed up in on a heroic because I was still playing this game as a consul gamer not like an MMO gamer. Thank you in advanced for the help.