How do I redeem a game on steam?

1. Please follow these instructions to activate a new retail purchase on Steam:
2. Launch the Steam client software and log into your Steam account.
3. Click the Games Menu.
4. Choose Activate a Product on Steam.
5. Follow the on-screen instructions to complete the process.

For more information visit the steam site - https://support.steampowered.com/kb_article.php?ref=5414-TFBN-1352