One person offers to organize the circle. They keep track of who gets what, what goes where, etc. They set the prices, they set the number of imps (an imp is around 1ml, so it's generally around 5 imps/bottle) and they place the order.
What you do on your end is tell the organizer what you want and pay for it. The organizer will keep you updated on when they placed the order and what the status is.
Edited to fix a glaring math error! ^^;