I presume flaming means to be inflamatory but what does trolling mean?
Trolls are people who join a forum deliberately to stir up trouble.
Some people do this on a full-time basis - it's their hobby. And they can be very skillful at this - some develop it into a kind of an "art" form, if one could call it like that.
They're rather painful. But luckily there's karma and the wheel will come round one day.