How do I watch HDTV on my TV set

If you attach an antenna to your TV, select over the air, and run a channel scan you will be able to watch free over the air broadcast TV channels. How many you get will depend on your location and the quality of the antenna.
You can use cable or satellite to watch HD channels,
You can use a streaming device such as a Roku, Apple TV, Chromecast, Firestick, or android TV box to watch HD.
You can use a Blueray disc player to watch the highest quality picture and sound. These will also stream HD from the internet.