I don't understand what to do in the Harpy Contract in chapter 2? and how to use Harpy traps?

Put the traps in your pocket. When harpies are around, just activate them as you'd activate anything in your pocket.. Geralt will place the trap on the floor, and a harpy should pick it up

it doesn't work..... for example i was surounded by Harpys and i have puten several traps and nothing happend.

Then you were putting them nowhere near an active nest.

Oh... i didn't know i have to put it near a nest.... the problem is i don't know where the god damn things are located..... well lets start searching :P

I hope you never actually did that. :/ Is it bad, that I'm still sitting here trying to imagine it though?

They fly across the entire area with them in that quarry or whatever it was, so it doesn't have to be near.

but when i have putten it in a certain place (near the crypt which is near the dwarwen town) they didn't take it and just attacked me...

If you set a trap near a nest that's already been blown up, then they harpy will just play with the trap, but won't carry it anywhere. Make sure to have the quest active in your journal, so you can see ?/7 nests destroyed.

You need to backtrack. Map attached.

All you need is harpies and traps, a nest doesn't have to be nearby, or, at least, visible.

I finished this quest by just traveling in the Quarry, and when a harpy appeared, I'd put down a trap, run away about 50-60 feet. They don't always take them, and of the ones that do only the regular harpies (not the elite versions) do so. In that event I just kill them.

Like I stated, though, I didn't bother looking for nests.

Also, something else I noticed, I could only get 4 of the 7 nests from the quarries. It wasn't until I went into the cave where the dream crystals are that I could get the other 3.

Oh, yeah. I count that as part of the Quarry, as I don't know what it's called :P

Also, the huge wilderness part by the river on the other side of Vergen has TONS of harpies, but no nests. That was a frustrating exercise in futility. I even saw a giant bird's next in a tower, and couldn't do anything with it. The witcher 1 was also famous for this kind of quest confusion. "OH, you mean THIS dirty swamp cave!"