How does a TV tuner work?

[oldcpu]

How does a TV tuner work? I do not see anywhere one can screw the cable line in.

Is the card itself all that is needed in order for it to work? No extra wires, adapters, or at least connecting to an antenna?

Do I have to pay some kind of service in order to receive channels?

[DoctorMO]

Er, tv isn't one thing. it's a whole bunch of technologies which you may or may not want to use.

I have a bt878 with on-board sound with a Philips analogue coaxial tuner; a frame grabber based pci tv card with an output of 640x400 perfect for PAL and NTSC traditional wide band transmitions of visual information.

The screw in kind are normally cable connections and a completely different kind of card would be needed to decode it.