Redeeming a Steam Gift is really simple, just follow these steps:
1.Enter the Steam Gift URL into your Internet browser.
2.Log into your Steam account.
3.Accept the Steam Gift by choosing Accept at the bottom of the screen.
4.Now choose if you want to add the game to your Steam Library or Inventory.
That's it, enjoy!
Note: Make sure to check your Steam Gift History!
The key is not working
If you have activated the key according to the guide but the code appears not to work, please check what type of error message you receive and depending on it follow the appropriate instructions: