The propagation of light can be seen as a series of blips, where energy expands and contracts around a line that is the direction of propagation. You could visualize it as an expanding and contracting blob that is symmetrical around the direction of propagation.  This can be considered as being composed of vertical and horizontal variations.  A polarizing filter only allows  light to pass in one axis, say vertical.  With two polarizing filters, one of which can be rotated, you can  have anywhere from half of the light getting through, when both filters are set to the same angle to none of the light getting through, when one is set to horizontal and one to vertical.  Get such a filter at a photography shop and try it. It is neat.

Glare is mostly caused by the light that is in only one of the planes.  If you put a single filter on your camera and look at the image while rotating the lens you will see dramatic effects.  Most photography that has dramatically blue skies is the result of such use of polarizing filters.  Learning to use polarizing filters can have a dramatic impact on the quality of landscape photos.  You don't have to understand the physics of light to use it.  I hope my explanation is comprehensible.  Mig could probably improve upon it.  

"It is not necessary to have hope in order to persevere."

The map was in the hand of a female :-)

_{*Lunatic*, n.
One whose delusions are out of fashion.}