Download and Start the STEAM Application (not Website).

Click on the + (or menu Game) and: Add a Game/Activate a Product on Steam (bottom left corner or menu Games) to activate the product on STEAM.

Click on the Next button, and on the I Agree button to move to the next step.

Copy and paste this code on the Product Activation Window or visit website: https://store.steampowered.com/account/registerkey?key=

Click the Finish button and from the Library install the Game (it will appear on your application) For more help visit this link:support.steampowered.com

To have a Steam account, you need to register on this website: store.steampowered.com

Click Download and install the Steam client. Wait for the installation process to complete.

Now, open the Steam client. Click "Add a game" and press the Activate a product on Steam to enable your activation keys on Steam.

You can now have fun with your game. For more support visit: support.steampowered.com.