How do I open it and play it?

Question

I downloaded it and installed it, but can't open the actual game and play it.

Answer 1

As far as I know, the Garry's Mod application requires for you to have the original game installed through Steam since it's steam compatibility. I have checked Steam and found out that this mod can be installed only on the original version of the game.

From the FAQ page:

Q: Why do I need garry's mod for Prophunt to work? A: Well, Actually Prophunt is a gamemode addon for Garry's Mod.

• Official page: https://steamcommunity.com/sharedfiles/filedetails/?id=135509255
• Buy Garry's MOD: http://store.steampowered.com/app/4000/