Go to http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2292168-five-nights-at-freddys-1-2-mod-v1-5-1-wiki and download it. Then download Forge and place the mod in the mods folder. Here is a video if you don't get it: https://www.youtube.com/watch?v=rUUW1KZNquE
What version of Forge, though? This needs to be made explicit somewhere.
1.7.10. I'll tell Rad right away to put that somewhere on MCForums.