To get audio and video from the RF signal provided by cable TV, you need a cable tuner of some sort (think of it as analogous to an FM tuner in conjunction with an antenna to hear radio stations). If you don't have access to a cable box and the TV lacks outputs, you need to find another device that offers a cable tuner. The easiest way to obtain this is a VCR. A simple "hifi" VCR (stereo analog audio outputs) will give you the outputs you want.

The problem doesn't crop up too often these days because satellite and digital cable both more or less require a standalone receiver and because analog (or even digital) audio outputs have become more common on TV's.