Nope, they're for carrying video signals much like an RCA cable can (in fact the two connectors can be swapped as you like as long as the format is the same.) They're far more resilient connectors though and lock in place - as oppose to the more domestic RCA connectors tend to be designed to be connected a few times in their life and then just left alone.
BNC cables are often daisy chained too, hence the in / out you've got there. Makes it easy to connect more than one display to the same source without running heaps of cables!
As such BNC is far more widely used in the pro video world where things need to a) be reliable and b) stand up to far more abuse than in the home - think tours, theatres etc. It's actually quite unusual to see them on home appliances at all, so just treat it as an added bonus if you should ever need to use it - though that is unlikely!!
If those are the only ports on the monitor it most likely doesn't have a TV tuner built in - and so you definitely won't be able to plug cable tv or an aerial straight into it and have it pick up channels, it doesn't work like that I'm afraid! You can pretty much think of BNC ports as the "professional" version of RCA, they do similar jobs but just with a different connector.
If you want to watch cable TV, you'll need an appropriate TV tuner card on your PC that you can plug the cable directly into.