So basically when you put up an auction you are giving something away for credits instead of money. At the end of your auction the winner will contact you with their address or any other info needed so you can send their item to them. When the winner confirms that they have gotten their item then thats when you recieve your credits.
if you send them in a bubbler mailer (oh and those only cost about 47cents) and put 1 stamp per an oz it wights then you should be good to go you can get them at walmart in there office supply section