Poisoner`s Anything?

What does the Poisoner do exactly? I have a Poisoner`s sword hilt and a Poisoners Axe of Axehattery that lengthens poisoning but does a person have to be poisoned first for my damage to work?

You can do damage with them without them being poisoned, however if you have a ranger primary or secondary, you can apply poison to the weapon and assuming your target doesn't eliminate it in some fashion, it'll effect them longer than if you hit them with a non-poisoners weapon.

I was wondering how much longer it actually lasts.

It's 33% longer. And to Olfin, I think the target has to be poisoned first for the lengthen poison to work (if that's what you were asking).

If you're wielding a Poisoners anything and you affect an enemy with poison (Ranger poison arrows, Necromancer poison skill like Necrotic Traversal) the poison duration lasts longer. They don't have to be poisoned already.