To install Garrys Mod addons you must right click your gmod icon on your desktop and select properties. Once through there another screen will pop up and ou then will look for steamaps>“username”>Garrys mod>Garrys mod>Addons.
Part Two) Then go to the addon you want and select “download mirror 1” and open it. after that drag the folder to addons! if it doesn’t have an info text click on the folder, if it doesnt have it still, it might need to go into JUST the garrysmod>garrysmod.
Same thing but instead click on maps then drag that to the folder unless told other wise bro!