Money on SwunkCraft is diamond based. A diamond is worth $10. You can withdraw and deposit diamonds while in the shop world. Currency can then be put in the bank to earn interest and be brought with you to all of the other non-shop worlds, or can be kept in the shops in your balance.
/bal - check your currency balance (balance is on a per-world basis)
/pay <user> <amount> pay the user an amount of money from your balance
Break Click on another person's shop
Preview the item being sold by hovering over the "Preview Item" tag in chat
Enter the amount you want to trade in the chat
Place a Chest
Break Click the chest with the item you want to sell
Type in the price for the item (as prompted) in chat
Fill the chest with the items you want to sell
Build click on the shop if you wish to edit the shop (change to selling mode, delete shop, change price, etc.)
/qs staff add <player> - allows a player to open your chest (and stock it), set price, toggle selling and buying. The staff cannot remove the shop or get money from the trades
/qs staff del <player> - removes a shop staff member
/qs staff clear - removes all staff members
/qs staff list - lists your staff members