well, the map probably came with the folders maps, and materials.. just put what ever file is in the maps folder into your.. maps folder, and what ever materials into the materials folder.. If its sounds, make a new folder named sound, and put what ever files needed in there. This is probably all explained in the readme that came with the map.. just a little info for the future.. Hope this helped
Edit: the directory im talking about is... C:\Program Files\Valve\Steam\SteamApps\username\counter-strike source\cstrike
place all the folder/files into the material folder..(C:\Program Files\Valve\Steam\SteamApps\username\counter-strike source\cstrike\materials) not any sub folder, and place the files located in the maps folder (that you downloaded), into...C:\Program Files\Valve\Steam\SteamApps\username\counter-strike source\cstrike\maps
I have to go to bed now, i hope this cleared some stuff up, and if not, im sure theres someone else here that will surely explain it a little bit more than I have...