1. Select the game merchandise you want and click Buy Now
2. Receive Steam Game Key code from seller
3. Login to Steam
4. At the top left, select the Games menu > Activate a Product on Steam...
5. Click Next until you find instructions for entering the Steam Game Key code
6. Enter the code you have received from the seller and press Next
7. Check if the code you entered is active
8. If so, go back to itemku, check your purchase history, and press Done on your order