You make a center block under 24 X24 and then the others in the group each take a turn adding a different size border. After all 5 borders have been added to your center block you get it back!
there is also a row robin on this site. That is when you do the first row and people add a row to yours making a quilt in the same way. You can have more people work on the row robin at a time since the rows tend to be smaller.