Thanks hwps a lot I was doing it all wrong

Hi there I'm new to MMOs altogether and was wondering what DPs suppose to do in flashpoints was told to hang back tank pulls the aggro then attack what the tank pulled does that sound wright swtor is my first mmo ever totally lost

was moving right along with the story line until I hit level 25 then the mob went from 3 to 6 and I get demolished quick and can get no further into the story what's a good way to handle the big mobs i'm a jedi knight and very much newbie