Through a TV Tuner card, if you have cable you may need a special one, if you want to use over the air tv broadcasts you can use that but you will need an antenna.
Here is alist of USB TV tuners
You may also be interested in watching television programs on a computer. This is also possible with the right wired or wireless equipment installed. Here are some instructions for watching tv on laptop without internet connection.
1. Install the Software (Its just a special DVD player App).
2. Get the Aerial and screw it into the corresponding slot on the USB stick itself (The Aerial plugs into the USB stick, NOT the laptop/pc, this baffled me for days, I just couldn't figure out where it was supposed to fit on my laptop, so you can thank me later for saving you the same anguish).
3. On the Blaze Software, Click Scan for channels and select your country to scan and leave it for a couple minutes to scan.
4. The Aerial base is magnetic (Something I didn't realize for months), so you can stick it to metal things around you, which will give it a much more stable signal and it will ensure it stays fixed in place, its quite genius really, I only wish I realized sooner ha
5. Wallah it should be working, you can either right click the video window and select channels to browse or you can use the remote that comes with it.