After added the base game , you can visit the giveaway page on the Paradox webpage.
Filled your Email into the blank shows below. if you do not have the Paradox account, Regist an account before subscribing.
After subscribed, refresh the current page, and click the link shown below, and you will find out the game key has distributed into your Paradox account
Active the steam key on the Steam platform.
Crusader Kings II: The Old Gods is the DLC of the game Crusader Kings II.
In many players opinions, this DLC is the best choice to enhance the game expirence.
Also before get it, you can check the game video
Northernlion Plays: Crusader Kings II: The Old Gods! [Episode 1]