I was in a round robin once, you make your first block and send it to your mailing buddy. You receive your other buddy's first block, make one to compliment it and send it along. At the end you get your block back with all the blocks made for you by the people in the round robin.
Only problem with the one I was in, the blocks all stopped at one person and we never heard from her again... LOL
Have fun with it, they are fun to do. :)