The player-controlled character is located near the center of the game screen. If you want to move, put your mouse in the place you want to go and left click.
Put your mouse on the NPC, and you will see them in the the following icon and click the left button.
Buy and Sell Items:
Go to the function NPC, select corresponding option to trade with NPC according to instructions and complete the transaction according to interface instructions.
Left click the Backpack, or use shortcut key B to open it. Then put your mouse over an item in the Backpack, left click or double-click to use it.
Left click to open Backpack, drag an item to the Discard panel, or left click to select an item and choose Drop (Confirmation required).
Put the mouse on the attack target, when the cursor turns into a sword, left click to attack.