Ok I'll bite.
First get your own damage meters running.
Then a) you can stop asking
and b) you can analyse what you are not doing.
Nowadays you can find yourself in dungeons with people fully decked in heirlooms and if you are as new to this as you sound then you won't be able to compete with them for damage.
The answer to your question is so wide as to be meaningless. I would suggest reading the sticky (up the top of the forum) and seeing if you are on the right lines.
For example it could be gear, it could be technique, it could be ammunition, if you posted a character name and server (or armory link) then it might be easier to spot the reasons.
Oh, and if its a sock-troll then sorry guys.
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Wherever I go - there I am.