To start the DLC content, you must first progress through the base game's main story:

The base cult area can be expanded to the south, providing significantly more building space.

While Woolhaven is a full expansion, other available packs for Cult of the Lamb serve different purposes: Cult of the Lamb: Woolhaven - Gameplay Walkthrough Part 1

Activation creates a permanent backup of your base save file, as the save becomes tied to the DLC once you proceed. Key DLC Features

You must manage a new Winter Mechanic where blizzards and freezing temperatures threaten your cult. You'll need to build and fuel Furnaces with a new resource called Rotburn to keep followers from dying of frostbite.

You can now breed rare animals like Yakish , Llamaish , and Cowish creatures to harvest wool and meat.