For Windows and Linux user:
Extract the archive directly into the working directory of Amnesia (this can be the redist folder, an amnesia the dark descent folder, wherever Amnesia is installed). For Windows users, run the BAT file located in the mod's directory. For Linux users, run the SH file located in the mod's directory.
For Mac users:
Extract the archive to Mac > Applications > Amnesia > Contents > Resources. To do this, go to Mac > Applications and right-click on Amnesia and click on open package contents. Then run the SCPT file located in the mod's directory.
If none of the system dependent script files come with the mod, or if they don't work properly, in order to launch the full conversion, you'll need to open up a terminal (or console or command prompt) and launch Amnesia through there, passing in the path of the full conversion's main_init.cfg as one of its arguments.
If you have Amnesia for Steam, you can create your own shortcut to Amnesia with the path of the mod's main_init.cfg as one of the launch options.