Most unlockers come with instructions. These usually involve copying files into your CK2 directory or running an executable.
When the game launches, it asks the Steam client if the user owns specific DLC IDs. The unlocker intercepts this request and sends a "True" response back to the game, tricking it into enabling the content. File Requirements: Crusader Kings II
: Only download tools from verified community sources. Scanners like VirusTotal often flag these as "GameHack" or "Trojan," which can be false positives, but caution is required.