Okay. I hope you understand if not - USE GOOGLE TRANSLATE!
The link you provide below lead me to a page saying "Oops! Page not found!"
I'm not quite sure what a "Product key" is but as far as I understand it's the Serial Code.
What I understand is that you're trying to register your game. What you need to do (assuming you have a Sims 3 account - if you don't... make one!) is go ahead to the "register game" button which will allow you to do so. You then need only to type your product key/serial code in the spaces provided and you're done.
Hope this helps!
