use a .txt file, write it inside(youn can use notepad++) and save it as a .hps file with the name of your map it should work on. Example:
map: test01.map
script file:test01.hps
you have to add the basic functions:
OnStart()
{
}
OnEnter()
{
}
OnLeave()
{
}
Then you can put the stuff inside and let wonders happen.
You have to either use the developer environment and place the .map and .hps files under amnesia the dark descent>maps>yourcustomstorynamehere>maps
Or make a custom story straight away, but you will also need a custom_story_settings.cfg file and possibly the extra_english.lang file(idk if that's optional or not). If you don't know how to make any of the both, you can either ask again or go to
http://wiki.frictionalgames.com/hpl2/amn...stom_story
Edit: .lang file is not optional