The jumper Silver Ranger referred to is in the cable coming from the outside connector. It must be in place AND the amplifier switch must be OFF if connected to the campground's supplied cable service. if using a satellite receiver, the in/out of the satellite receiver replaces the jumper, again the amplifier switch is off.
Now for tv reception... Unless you are in a strong signal area, the antenna should be up and pointed in the direction of the transmitter. The amplifier switch must be ON. The green, or maybe red light next to the switch only indicates the switch is on and
12v is available to the amplifier. On late model Winegard Sensar antennas, the amplifier is actually located in the white plastic housing on the antenna itself. A bad coax connection at the antenna or any connector on the back of the switch or to the antenna terminal on the tv can be a problem. suspect the one on the roof as it is exposed to the elements, but more often the problem can be a simple menu setting on the newer tv sets. if you get at least 1 channel, your connections are probably ok, but make sure they are clean and tight.
Analog vs. Digital... In most locations, the tv signal is now broadcast in digital format. Any antenna capable of receiving UHF broadcasts is all that is needed. The common Winegard Sensar is perfectly adequate. The menu on the tv must be set to antenna, not cable and digital, not analog and a channel scan needs to be run on most tvs before reception is possible. Here's the big gotcha: in some locations, it is necessary to point the antenna towards the station(s) before running the scan. I've been at locations where if the antenna was off as few as 3 detents from dead on, it would not find any stations during the scan. Other locations have been more forgiving. Look at where your neighbors have pointed their antennas and set yours the same and you at least stand a fighting chance. If the channel freezes and pixelates, try turning the antenna a detent or 2 one way and then the other to see if that is better. Some TVs have a menu option to display a signal strength meter to assist in centering the antenna. The old analog tv signals degraded gracefully, there might be a ghost or snow, but you could often improve the signal by turning the antenna. Digital either works, or doesn't. If right at the edge, you will experience freezing and pixelation. If pointed the wrong way, or too far from the transmitter, you may find nothing.
In some rural areas, repeaters and small stations are still broadcasting in analog. In that case, the tv needs to be switched to analog mode. As above, antenna not cable must be selected and the amplifier switch must be ON.
If this seems frustrating, welcome to the club. We camp monthly with a local GS chapter and I have several fellow members who have trouble every month, so I make the rounds helping them get set up so they can watch their TVs.