The trading aspect of this challenge is quite simple, all entrants submit one ATC and at the deadline the list of entries is randomised. This random list is used to decide who trades with whom. It is a sort of blind swap since you do not know which ATC will be coming your way. If this sort of trade interests you, then why not join the site and see if you can find more to interest you. We have many groups (mixed media art mostly) with a number of different activities.
Here are the entries for the 37th challenge, the theme was spring:-
the first from a digital source by Kaylene