A polarizing filter is a useful addition to your photography kit. It helps reduce reflections and glare in the same way as polaroid sunglasses.
Unlike many other filters you have to rotate the filter to find the best angle to reduce the glare or reflection.
A polarizing filter also helps enhance the blue in the sky which can make your photos stand out. Again you will need to adjust the angle of filter by rotating it.
You do need to be aware that polarising filters do reduce the amount of light coming through the lens so watch your exposure.
Here is my video tutorial showing you how it works and some examples.