How can you get the sound from your tv to come through your audio system speakers?

Your TV will need to have some sort of audio output. Some do, many don't.

A dedicated audio output on a TV will usually be an analog stereo mini jack connection, or a newer model may have an optical or coaxial digital audio output. These will need connecting to an audio input on your sound system amplifier.

If your TV has a headphone output, you can sometimes connect this to your amplifier and get a reasonable sound.