For my birthday my parents got me a polarizing filter for my main lens. I wanted a polarizing filter mostly to reduce the reflection on water so I can get photos such as this one. But polarizing filters will reduce reflections on almost any surface, save very glossy ones and mirrors. They also will create a darker, more rich sky when the sun is at your back. This is because reflections and certain skylight contain polarized light. Polarized light is light waves traveling in the same direction in the same orientation. A polarizing filter or polarizing sunglass lenses block out this light by not allowing the waves traveling in that orientation pass through, therefore reducing any reflection coming off water, a street, or anything. Now that I have confused you thoroughly, take a look at this diagram and maybe you will understand it a bit better
