Please check your mail for the code (can check your spam mail as well).
1. Visit this Microsoft Regarding Redeem(https://redeem.microsoft.com/enter?ref=xboxcom)website. you will be faced with a login page for your Hotmail/Outlook e-mail, please Login first.
2. You have entered the last stage in redeem, Enter the Voucher Code attached in the previous e-mail, click next after you have finished entering the code.