Need help installing mods/Folder isn't there

I just bought Garry’s Mod recently and I wanted to install some mods. Many how-to’s and youtube videos say to go to program files/steam/steamapps/yourname. Problem is that when I go to steamapps there isn’t a folder with my name on it. There are only common, downloading, sourcemods, and temp folders in it. I checked all of those folders and I can’t find any folder labeled garry’s mod or with my name. Does anyone know what the problem is?

If you haven’t launched it yet, it won’t create the username/garrysmod folder.