i’ve never actually participated in one (yet - i’m thinking about joining a HP sock swap), but i’ve checked out a bunch of them. all the swaps i’ve seen are blind, like a secret pal kind of thing. i don’t know if this is how they all are. with some swaps you knit an item and send it to a recipient. (someone does the same for you.) with yarn swaps, you send someone some yarn and usually some accessories to go along with it, and you get the same back. i’ve even seen a sock kit swap where you send someone sock yarn, a pattern, a hand/homemade bag, needles, and accessories (or even edible goodies). they sound like a lot of fun.