compUterscUter Yes, You can use both laptops screen and monitor at same time.
or just monitor only. It's too easy. No third party apps needed. Mac/Windows/Linux they all handle external monitors effortlessly. Make sure your laptop is not too old (old ports). Otherwise, its just plug and play.
Monitor as a TV, yes. if the set-top box supports HDMI. For Cable television to work monitor you’ll need a TV tuner box.