I was asked by someone recently what a polarizing filter does and was it worth paying so money much for one? Well, the only way to answer this question is by example, so I set up, with a little help from God and nature, a perfect test area with a huge amount of reflection on wet leaves coming from the diffused light of the sun. Please note, these are for test and display purposes only and are not meant to look remotely pleasant to the eyes.
Here is the special test area unpolarized:
The leaves are wet and reflecting a lot of light into the lens and giving much less than desirable results. Or to use a highly technical term, "it looks yucky"!
Here is the exact same scene, a few seconds later, with the polarizing filter applied. It is simple enough to use, you simply rotate it until the shine goes away! Just remember to look through the viewer while you are doing this or you will not be able to see when you have achieved optimal effect. Live view works just as well.
The first thing you will notice, of course, is that the shine is gone! Vanished into thin air! The second thing that you will notice, is that the greens of the leaves are beautifully saturated, and the picture just looks better in every way. All that shine plays havoc with metering and exposure.
If you intend to photograph gardens, landscapes or shiny cars and buildings a circular polariser is a great idea that will assist you to get much better results by taking away the shine. In landscapes it will also give a beautiful deep blue sky, but it may not look great using wider lenses because the polariser will only turn part of the sky dark blue and it could all end up looking a little strange. Some people like this effect and do it on purpose.
Please note that the polariser reduces the amount of light entering the lens and so in low light shutter speeds may drop too low to hand hold requiring you to use a tripod.
Happy light hunting!