How to watch TV on Computer???

Hi,
i've got a TV-out in my computer, and i want to watch TV on my computer. I bought a cable to connect the computer to the socket in the wall, and i conneced the computer using the cable to the wall's socket, but nothing happened. I can't watch TV on the Computer!!! WHY!!! Do i need a special software!!!!!
PLEASe helppp!!!

TV-out
not
TV-IN
:)
لازم تحصل على كرت به مدخل فيديو او تيونير

كرت في tv in ما بكفي ، انت بحاجة الى كرت تلفزيون خوصي او كرت اي تي اي All in Wonder لانه في عليه تيونر تلفزيون يا شاطر.....!!!!؟؟؟؟":"

Thanks all!!!