I have a 19 inch element tv that I have used before as a tv a few months ago I bought a bigger tv and left it unplugged till last night and I only have rf channels not sure why but I need to have cable channels instead.
If you are not using a cable box then you will have to run a channel scan before the TV will tune any channels. You will only get unencrypted channels if there are any.
If you are using a cable box it should be connected with HDMI or AV cables not to the antenna input. Some cable providers have a digital accessory that is cheaper than a cable box to rent.