Under the manage trade button should be a "specific trade" button where the trainer puts his stuff up for trade and fills out a "specify trade" box where they type in what they are looking for (pokemon wanting, level wanting, etc). For example: I put up an emboar lv5 from my list and say that I'm searching for servine lv10. So when the trainer who sees this wants that emboar and will not mind giving up servine clicks on it, it will initiate a trade between the two.