Jacquie, each set has one 1.5" square of fifty different fabrics. We sign up for how many 'sets' we want to trade. If you send 2 sets, you will get 2 sets back. I believe the limit for this one is 25 sets.
This is my 4th swap, I am working on setting up 26 piles near my cutting board. I always make a set to give to Missi.
Yes, they need to be from washed fabrics.
It is also a good idea to put them in a baggie of some sort (each set that is) and have your name and board name marked on it each baggie. Swappers do different things here also. Some sew a double thread through an entire set and put a label on it and some skrink wrap each set, etc. Let us know if you have other questions. :-D