The TV tuner card slid into the computer on rails. If I recall correctly, there was one ribbon cable that connected to the tuner card. It had a small opening to the outside world, which without the card installed looked like a circle was meant to be punched out of it. That circle indicated the position of the coax connector for cable or antenna.
If you are looking for the card, check on eBay. Lots of vintage and out of production parts are there.