-INSTALLATION FOR NEWBIES-
First, obviously, you download this.
Go into your computer folder and click on LOCAL DISK.
Then scroll down to Program Files and click on that. When inside Program Files, scroll down to Steam, click on Steam and go to Steam Apps. You should find your steam name somewhere in that folder. Click on it and then go to your Counter-Strike Source folder. Click on it and then go to cstrike. After that, copy paste your maps folder into the cstrike folder. (The maps folder is inside of the ZIP you receive from downloading this.)
After that, you're done! Congratulations you have successfully downloaded the map. 
You do this with everything else. Even skins and models and etc. [I have a Windows 7 Operating System. This installation instruction manual should work for everything until Windows 2000, which nobody should be still using to play Counter Strike: Source.]
-INSTALLATION FOR NEWBIES-