Garrys Mod Content

[rlm850]

I've never setup a garrys mod server totally on my own before. How do you put in content from games like CSS, TF2, etc to be usable from the props menu? I would assume copying the entire game files into the garrysmod folder, but wouldn't it end up overwriting other files? Then I remembered I used to see counter-strike, team-fortress folders in the addons folder, but have no idea what to do.

Any help would be splendid.