noobings: DLed models not showing?

I apologize in advance for asking what probably seems obvious to 90% of the users here, but after scouring about as best as I could, I can’t seem to find a how-to for placing new/replacement models for the player OR for NPCs. There are some very good write-ups and links for Addons, which I’ve looked at, but they didn’t seem to apply to adding models. I’m running a freshly installed, legit copy of GMod 10 on a system that goes something like this:
AMD Athlon X2 3.0GHz
Nvidia 8600 GT (yes I know it’s old, I’m saving up to do a new mobo and GFX at the same time)
4GB RAM
Windows Vista Home Basic

…The game runs fine, but I’ve tried unzipping the model packages into a few different folders (including /garrysmod/garrysmod and /garrysmod/garrysmod/addons and garrysmod/garrysmod/models …etc etc), with no success… any ideas?

Thanks.

have you tried searching for your models? also near the search bar, there is a button to rebuild your search cache, try both of those.