1. Unrar/unzip the archive directly into your custom_stories subfolder inside your Amnesia game directory. For Steam users, this would be:
C:/Program Files/Steam/steamapps/common/amnesia the dark descent/custom_stories
For retail:
C:/Program Files/Amnesia - The Dark Descent/redist/custom_stories
2. That's pretty much it! The mod should now appear as "Emma's Nightmare" in the Custom Stories button in the main Amnesia Menu.
3. Enjoy!