1.Operation

Click on up or down arrow on the right to view more goods in the shop.
Click on X on the top right corner to exit the window.
Stop your cursor on an item for detailed information including the price.

2. Buy items:

There are two ways to buy items:
A. Right click on the item you want to buy, if you have enough money, then the item will come to your inventory automatically.
B. Drag the item you want to buy to your inventory. If you have enough money, the item will be in your inventory.
If you do not have enough money for that, the buying is failed.

3.Sell items:

Drag the item you want to sell to the goods window of a trading NPC.