Without the model of the TV or stereo I will guess that your TV doesn't have analog L/R audio outputs. It might have inputs that look the same.
Most TVs have an digital optical audio output. If your stereo only has analog RCA inputs you will need an active optical to analog converter.
Check the TV manual on how to configure the TV to use that output. You may need to turn the TV speakers off and change the audio output to PCM stereo in the TV menu.