You look at the back of your PC and you will see slots, some may be blocked off, others may have sockets and stuff poking out. Where there is stuff poking out they are from cards that have been slotted into sockets on the main computer board *i.e. the motherboard).
Those sockets will be connected together and those connections are referred to as a bus, in the case of today's computers the commonly used bus is the PCI bus.
If you want more facilities on your PC (in this case I'm referring to a TV card, but other cards are available) you can purchase the card you want, open up the PC, slot the card into the socket, and then close up the PC again. On next reboot the PC should realise it has something extra and spend a little time changing its settings etc. so it can be used.
My woman has a TV card in her PC, uses it to watch when she is doing her ironing (in the study). Once the card had been installed all that was necessary was to plug the aerial lead in the back (into the card) , and to install/run the software. But I can not recommend the card she has as the company has now gone bust, which is a pity because it was a reasonable product, well recommended at the time.
Try checking Google or Wikipedia for more info, or try your local PC shop and ask to browse their PCI cards.