Liquid crystal displays (LCD's) work by filtering polarized light. If you hold two polarizing filters (or polarized sunglasses) against each other, and rotate one of them, at some angle no light will get through. That's because light gets polarized by the first filter, and then the polarized light is at the wrong angle to pass through the second filter. LCDs insert a special liquid in between the two filters. The molecules in this liquid are twisted like a screw, and they rotate the polarization of the light as it passes through them. Then the light can pass through the second filter. If you then apply a voltage across the liquid, the molecules are untwisted. Then the polarization of the light doesn't get rotates, so the second filter blocks it.

Also, if you look closely at an LCD screen, you'll see it's broken up into thousands of tiny dots called pixels. Every pixel can be individually controlled by the TV to turn it on or off. We get colors because there are 3 types of cells: red, green, and blue. All 3 need to be turned on to get a white pixel.