Every tv signal comes in at 60hz
LCDs/LEDs have a problem with fast motion(Sports, actions scenes, scrolling text)
What 120hz does is double the hz or refresh rate. So you get 60hz twice every second. By doing that you get smoother motion during sports, actions scenes, scrolling text etc.
240 is 60hz X 4 every second. Which is supposed to give you the smoothest motion. But from all reports there is very little difference in terms of blurring between a 120hz set and 240hz set
Some LCDs/LED have a by product of the motion flow/smooth motion effects manafcatuers employ. Which gives it the soap opera effect, turning movies into video camera shoots. You can turn it down or off though