Put a itemstack of your choice into the marked (left, with the lock symbol) input and another itemstack into the output slot. Then place a (Personal) Chest nearby and fill it with itemstacks equal to the output (Note: The stacks must be equal in # of items, item (ID) and damage-value!).
Any other player (including yourself), can now drop a itemstack into the public input slot. It will then be traded with a output.
Imporant limitation: You cannot trade 1 dirt vs 6 iron (Example) by dropping a stack of dirt in. One would need to place a single dirt into the input to perform the trade.
