Arduino Sound Sensor Need Help

I need to know if and how I can connect an arduino to a TV or audio device and detect the sound level from the cable or wire coming from the audio device to the arduino. I would appreciate the help as I just got my first Arduino board last night. I've gotten through almost all the tutorials.

There is a schematic: http://interface.khm.de/index.php/lab/experiments/arduino-realtime-audio-processing/

Thanks for the help. That’s what I was looking for.