I have a tv hookup in BR. If I connect a cable to it and put up antenna, I get "over the air" reception. If the campground has cable at the post with water/electric and I connect a cable from my fiver...
As stated there should be a switch near your TV where your antenna, cable hookup and TV are connected. Usually an LED light on it shows when the antenna is on. Push this switch and LED goes off indicating the TV is now connected to the outside cable connector.
You will then have to use your TV's menu to tell it to scan cable channels instead of over the air antenna channels.