truehell file

Step 1: Download the file.

Step 2: Extract the file with a program like 7-Zip or WinRAR.

Step 3: Buy The Ultimate Doom from steam.

Step 4: Download GZDoom.

Step 5: Put your Ultimate Doom WAD in the GZDoom folder (The WAD should be called "DOOM.WAD")

Step 6: Drag truehell.wad in the GZDoom folder.

Step 7: Drag truehell.wad onto the GZDoom executable.

After that you're good to go. IDDQD and IDKFA cheats required.