just WHAT is gmodstore?

Basically, there's the Steam Workshop which provides free addons, such as cars, guns, playermodels, etc.

However, "gmodstore", formerly known as "ScriptFodder" is actually a plugin/script website. You're there to buy scripts for your server(s) or whatever. You won't be finding guns, playermodels, cars, etc.
Although, you will be finding Scoreboards, Loading Screens, Logging Systems, Admin Systems, Inventory, DJ Kits, HUDs, Gamemodes, NPCs/Vendors, and a whole bunch more of stuff like that.

Reason you have to pay is; Developers put hard time into their work and they want to be paid for it, pretty common principle;

> Work hard on something.
> Put it up for sale.
> Make money.


I hope this explains mostly everything you were asking.