It's built in and you record things called demo.
Open your console then type: "record " (without quotes), this will start recording a demo. To stop recording, bring up the console again and type "stop". The demo will now be complete and is saved in your Steam\SteamApps\counter-strike-source\cstrike folder named .dem.
There are some programs that convert .dem into .avi , but i had to search a while to found one and it wasn't of good quality.
So i recommend recording a demo, playing it in css , and then record that with fraps.