Depends on the TV. If it has a tuner built it then all you need is an antenna.
If the TV doesn't have a tuner then you'll need a antenna and a tuner.
If you are in the US there are a couple sites that can help you choose an antenna and which direction it should be aimed(if it's directional).
https://www.antennaweb.org/
http://www.terk.com/antenna-finder/