With a TV tuner for a laptop you can watch TV using an antenna or from a cable or satellite signal. Tuners are also available that are compatible with analog, digital and high definition (HD) signals but currently, HD signals from an antenna are the only ones that tuners can process.
To watch shows on cable or satellite your computer must be in a location with a cable from your cable or satellite TV provider. All over the air channels are now broadcast in digital and some programs are even broadcast over the air in HD. Over the air programming is limited and quality varies based on your antenna and how far you are from a transmitter. However, an antenna allows you to watch TV where there is no cable or satellite. Some tuners have built in antennas and most come with a portable antenna and upgraded antennas are available for under . If you plan to watch a lot of over the air channels an upgraded antenna would be a good idea.
Cable channels such as HGTV and CNBC are only available when using a cable or satellite signal (not an antenna) and if you subscribe to premium channels such as HBO you will need a cable or satellite converter box. The box is installed between the TV signal and the tuner. More and more channels are being broadcast over the air in digital format (Clear QAM) which some tuners can process without the need of a converter box.