Rising Tide is an exciting expansion to Civilization: Beyond Earth which introduces oceanic gameplay, extending the play space to the entire surface of the planet, greatly enhanced diplomacy as well as hybrid affinities, new factions, and expanded game systems.
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