You can deposit 20 items in your warehouse.

You have a warehouse in every city and warehouses in every city are separated. In another word, you can only retrieve your items from the exact warehouse where you store them, but you can withdraw your money from all warehouses.

Access a warehouse:
Left click on the warehouseman, both your inventory and the warehouse window will pop up

Store items
Drag and drop your items into the warehouse slots

Retrieve items:
Left click on the item you want to withdraw, it will be taken back to the inventory.

Deposit money:
Type in the box the amount of money you want to deposit and click on Deposit button.

Withdraw money:
Type in the box the amount of money you want to withdraw and click on Withdraw button.