assuming the person reading this is a steam dweller who hasnt modded anything using outside sources you will need to go to the hl2 gamebanana page of this model download it and when you do that create a file called "models" inside the materials folder and place the og folder that was in there in said folder and you just wanna put those two in the addons folder that should be found like this C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod