Omega 3s--nearly all of us in North America don't have enough of. It's anti-inflammatory.
Omega 6s--we need them, too, but in modern North America diet, we get way too much of the 6s. They are inflammatory, so they cause disease if they are not in balance with the Omega 3s.
Omega 9s are neutral as far as I know--neither inflammatory nor anti-inflammatory. Someone correct me if I'm off base here. I don't think there' s any need to take 9s at all for inflammatory or anti-inflammatory purposes, obviously.
As for how much omega 3 you need, that is very individual ... I think I'll wait and see if others can explain this part ...
But if you just need to maintain, and are on the zone diet, you only need 2.5 grams of fish oil. But if you have health issues, you'll need to research how much you need. Hopefully someone can give you the information here, I can't seem to find it at the moment.