You can redeem the Steam Game codes through the Steam Website or the Steam desktop application. Here are the steps you can follow:
Through the Steam website
- Visit the Steam Product Activation page (Make sure to log in with your account first)
- Enter the code you have purchased in the box, check the Steam Agreement check box, and click the "Continue" button
- Follow the instructions until the activation is successful
Through the Steam desktop application
- Open the Steam application and log in to your Steam account
- Click the "Game" menu and choose the "Activate a Product on Steam" option
- Click the "Next" button
- Read the agreement and then click the "I Agree" button to continue
- Enter the code you have purchased into the box and click the "Next" button
- After the activation is successful, click the "Finish" button. Then you can proceed to your Steam game library and install the game that you prefer