I finally understand!!! Yeah for me. Now were's the swap page?Pretend that Ann has Apples for the current offer. Bob wants the apples so he says "Mine". Bob offers bananas. He then sends a PM to Ann stating he claimed her apples and gives her his address. Ann ships the apples to Bob with a delivery confirmation number. Ann pays to ship the apples.
In the mean time, Connie is craving banas so she posts "mine" and offers chocolate. She sends her info to Bob via PM and Bob ships the bananas to Connie with a delivery confirmation number. This chain just continues.