You can move your character by mouse as well as by keyboard.

Mouse: Left click destination ground to move the character there.
Keyboards: W: forward, S: backward, A: step left, D: step right, Space: jump.

NPC with a "!" mark over its head means this NPC has quests for you to accept. Right click to talk to him, and accept quests.

NPC with a "?" over its head means you have finished quests. Right click to talk to him, finish quest and get your rewards.

Click "Quest" button on the menu bar (or press short-cut "L") to open quest list.

Check "Trace" on quest list interface, then the quest will be shown on "Information Navigation" pane.

Right-click to normal-attack a monster automatically; or left-click to choose a monster, and then use skills to attack it. Left-click the skill icon on skill bar to use skills.

Press key "Enter" and a chat input box will pop up.  Choose the channel you want to speak in by clicking channel button above the input box.  Input your words, press key "Enter" to send it out, and your message will be shown on the chat box as well.

Right-click the avatar of a player who is in the same faction with you, and select "Invite Team-up" on the menu bar, then an invitation box will pop up on the player's game interface.  If he clicks "OK", he will join your team; otherwise, if he clicks "Cancel", he won't join.

Right-click the avatar of a player that you want to trade with and select "Trade" on the menu bar, and then a trade prompt box will pop up on the player's game interface.  If he clicks "OK", trade interface will pop up for both of you.  Put the item that you want to trade into your own trade bar, and click "Lock" after you confirm the item.  After both sides are locked, click "Trade", and then the trade will be done.