You have to buy a tv tuner card compatible with your monitor and with your tv service provider to which you have subscribed.This tuner card will have a separate remote control where you have to press the "instructed" number for tv, to install the system and establish the connection between the devices.
There will be several modes available, among which you have to go through the trial and error process for a few minutes to see which one works better for you, if you are not going for an external professional help, and want to do all by yourself.
Each time you switch on the power plug, you have to first switch on the tuner card, then you have to switch on the tv set top box.
If you are still a cable tv viewer, you have to do this with the help of your cable tv operator.
One thing before buying. You have to give your monitor details, tv subscriber details to the shopkeeper and ask for the compatible tuner card.
This is from my current personal experience. When we upgraded our PC monitor, we had to change the TV tuner card as well.
It would cost around Rs. 500 - 1100 depending upon the model of your monitor.