Each swap is different. The host will give you all the guidlines in the swap post. If there are 25 participants, then you would send 24 items because you don't need one of your own back. The size of the item, or sample will be given in the swap guidelines. Next time there is a swap, just read the post and see if it is something you are able to do. Be sure that you are willing and able to follow thru with a swap before you say you will do it.