Downloading addons ( Sweps, Maps, Game modes, etc. )

Garry's Mod general
#1

So i havent been playing Gmod for quite a while now, decided to start playing again.

I wanted to start downloading addons, but i remember in the past it never worked for me.
I am running Vista for my operating system if that makes a difference.
What i really need to know, is how to download addons, what location to save them to.
i think it was something like

C:\Program Files (x86)\Steam\steamapps(my username)\garrysmod\garrysmod

or is it

C:\Program Files (x86)\Steam\steamapps(my username)\garrysmod\garrysmod\addons

#2

Yes, second one is where to install the addon, to tell if its an addon is to go into its main folder and see if it has a info.txt in it.