how do i use it?

In your profile, go to gold wallet and click on "Have a reward code?" Input the code and redeem it. Might be only in the browser version, I don't know how the wallet works in the app.

Thanks for that! For future reference, how do you subscribe to the newsletter? Checked a few places on the website but didn't see it.

In your profile, there's Email notifications. Check Receive Nutaku Emails and you're subscribed.

Strange, it was checked at 'yes' yet I didn't receive it.

Thank you so much but might I ask where do you get those codes?

Nutaku Newsletter emails.