LCDs are made up of linear polarizers from what I understand. If you think about polarizer filters on a camera lens then you know when you move them 90 degrees from the light the light cannot get through. LCDs work exactly the same. The polarizers are 90 degrees from the light source. However from my reading it appears that once the polarizers are at a 90 degree angle from a light source the "liquid crystals" are twisted which then allows light to pass through. Once the electric field is passed through the crystals the twist is removed and light stops passing through producing a black area.
Google is totally my friend.