Browse to your Steamsteamapps folder and check if you have a sourcemods folder there. If you don't, create one.- Unzip the file to your Steamsteamappssourcemods folder.(When you did this you should have a portal_stories_demo folder in sourcemods. In this folder there should be various maps like cfg, maps and materials. If this folder has another portal_stories_demo in it instead of the other folders, cut the content from the portal_stories_demo/portal_stories_demo and place them in the steam/steamapps/sourcemods/portal_stories_demo folder.)- RE-BOOT STEAM- You should now have Portal Stories Demo on steam! - Launch the game and enjoy!We really hope you enjoy this map!