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Can anyone tell me where I can code?
If you're talking about actually coding the game, you can't.
If you're talking about redeeming a code, you can log into your W101 account, look under the tab that has your username on it, and you should see a clickable link that says, "Redeem Card or Code". Input your code into that, and you'll be able to retrieve the item in-game. (It will have a notification on your screen when you log in.)