1. In order to activate a Google Play gift card, you will need to have a Google account (you can create one here)
2. Then you will need to login into the Google Play Store (you can find the website here)
3. Once you are there you should be able to find a "Redeem" button.
4. After you pressed the "Redeem" button a window should pop in which you will need to enter your Gift card's code.
Please bear in mind that your gift card must match the region/country you are in. We suggest to always check the restriction of the gift card.