A polarizer filter is amongst one of the most useful filters available in photography as what they offer can drastically improve the quality of your images if used correctly.
Polarizer filters offer many advantages such as polarising a blue sky 90 degrees to the angle of the sun, getting rid of non-metallic reflections such as on glass and on water as well as having the ability to saturate colours.
But how does this all work exactly? Well, first of all, we have to understand how light works. Light is a collection of light particles called photons which can be described as a wave that can undulate both "up and down" and "left to right", unpolarized and polarized light, respectively.
A polarizer filter essentially takes polarized light and converts it to unpolarized light, or filtering out wavelengths of light that undulate side to side which is what happens if light is reflected off of glass, water and other non-metallic reflections.
So for example, if you observe a body of water, perhaps a lake, you would be able to see the reflection of the sky and clouds on it, because of the polarized reflected light. If you were to unpolarized it by looking through a polarizer filter, you would now not be able to see the reflection on the water, but rather through the water.
Take a look at the video below by the YouTube channel: Michael The Maven on How Do Polarizer Filters Work?...