"GMOD," or "Garry's Mod," is a sandbox-style game made with the "Half-Life 2" engine. Players have open-ended game play and no limitations for creation. The objective and goals of the game are left completely up to the players, with infinite tools at their disposal. Players can add extra models, skins, items and add-ons to the game to diversify game play. Adding extra models will give you more nonplayable character choices, allowing you to be more unique situations.
Download the skin, texture, item or model that you wish to add to "GMOD."
Open the downloaded file, and extract the contents somewhere on your hard drive.
Open up the "garrysmod" file on your computer, located where you installed the game on your hard drive. Locate the "models" folder in the "garrysmod" directory, or if there is not one, create a folder with that name.
Put the contents of the downloaded file in the "models" folder.
Copy the contents of the "Addons" folder in to the "garrysmod," replacing any files that have the same name.
Load the game and select the model that you just placed in the "garrysmod" folder from the in-game menu.