So this is a little tutorial to download and extract any garry's mod addon which is really simple.

First you have to get your addon so

Step: 1 subscribe the wanted addon
Step: 2 go to your garry's mod file.
to do that you can just right click on garry's mod in your library and you click manage>browse file location (im not sure if it that my language is french on steam because im french)
Step: 3 go to garrysmod>addons and choose your addon.

After all of that done do Step 2 but instead of going into garrysmod again you are going to go into bin and after you are going to look for a file called gmad.exe
all you have to do now is to drag and drop your addon (.gma file) on gmad.exe and it should extract your addon into a file so you can configure or modify any addon you want on the workshop