Yeah, there was a pop-up on the bottom screen all like "Do you want to make a Wonder Trade?" and I'm like "I don't know what that is, but okay."
Apparently you put up one of your pokemon for trade, and then it searches for someone for you to trade with, and you get whatever pokemon they offer up (they don't know what pokemon you're offering, either). It was kind of interesting. I've done it three times so far. I go an eevee, a zubat, and a litwick.