liquid crystal and light
Liquid crystals are controlled by electric fields and their structure manipulates the polarisation of light
Liquid Crystals are usually made from long rod-shaped molecules which behave in some ways like liquids (they flow) but in other ways like crystals (they form structures with a lot of regularity). The name is appropriate.
The key features that matter are that the structures they form are easy to manipulate with electrical fields and that the rod-like nature of the structure interacts with light in roughly the same way as polaroid: it selectively alters the polarisation of the light passing through.
In LCD devices the liquid crystals are placed between two polaroid filters and in front of a backlight so the the default orientation of the filters plus the liquid crystal layer lets most light through. When a small electric field is applied across the liquid crystal it can be arranged so that it changes the orientation of the molecules in the layer and twists the light so it no longer passes through the polaroid layers. This can be arranged to happen one pixel at a time with suitable electronics. So an electrical field can drive a display.
That's the basic principle. Real displays have evolved to have some very complex arrangements of these effects to improve speed and the twistiness of the LC layer to make faster responding and higher contrast pixels.