Let me quote the content of the manual, which usually I put to the files (unless I forget to put it there): Paste "materials" and "models" to folder MLPPack located in Steam\SteamApps\<username steam>\garrysmod\garrysmod\addons
Alright, let's see. To properly install the model, copy the 'materials' and 'models' folders into the 'MLPPack' folder in your garry's mod addons. To spawn the model, go to the 'Browse' tab, look for 'MLPPack', and click on it. The model should be there. If it isn't... I just don't know what went wrong!
After downloading (as in taking the data off the internet) it, yes. A .rar file. After putting the model into the garry's mod files, no, it's in the same file as the other MLP characters. If you don't have said characters... well... you should download them.
Ok, here's a better idea; tell me the step-by-step process of how you put the model in the gmod files. It'll be much easier on the two of us if I know exactly what you did.