Little Big Adventure (also known as 'Relentless: Twinsen's Adventure') is an action-adventure RPG designed by Frédérick Raynal. It offers an epic story, quality puzzles and hundreds of characters and dialogues.
Open the Steam client, login and locate the Games tab on the top menu. Click this and then select “Activate a Product on Steam…”
Enter your unique code that's displayed on the 'Orders' page of CDKeys.com and follow the prompts to activate.
Your game is now viewable in the “Library” tab and is available to download/install when you’re ready. You can find additional support for the Steam client here: https://help.steampowered.com/en/wizard/HelpWithSteam