Full documentation of all the aspects of the HPL2 Engine by Frictional Games

1. Download & Read about the Tools.
2. Investigate how to setup a dev environment.
3. Read up on making a Custom Story.
4. Make sure you add a default script file to all your maps, as shown here.
5. Check the rest of the Tutorials.
6. If you get started with scripts, then the Script Functions page is a must.
7. Having problems with the tools? look for a solution on the Troubleshooting page.

Specific information on Script Functions available in Game Specific - Amnesia

HPL2 comes with a great set of Tools to ease the development.

Tutorials for all tools, scripts and engine usage.

Information on Third Party Tools that can be used to create models, graphics and art for the game and what specific things you will need to setup to make it all work.

Additionally there are plenty of Resources available, including upgraded tools and script libraries to aid in development.