Installing a mod
Run source2mod at least once, to create the required directories. Extract the mod folder to
Steam\SteamApps\source2mods. Run source2mod.exe at least once and select the mod you just installed. Restart Steam and the mod should show up in the Steam listing. Keep in mind you still can run the mod using the source2mod.exe file, or by creating a shortcut to source2mod.exe with the -game parameter.