Not long ago we wrote about a cheat sheet for polarising lens filters, which is perfect if you already know the ins and outs of filters and how they're used. If you want more basic advice about these wonderful devices, Mark Ryan Sallee of Michromatic is here to help.
As Ryan Sallee explains, the point of a polariser is to give you more control over lighting in situations where there's little else you can do (such as being outside). He also breaks down what the filter is actually doing to help balance out the colour in your photos:
Let's imagine that this polariser has a bunch of vertical bars -- kind of like a gaol cell -- and let's say the light coming from the sky is travelling with a horizontal polarity (it's moving left and right). The gaol cell bars of your polariser, basically, they're going the opposite direction of this polarised light, so they're actually going to block out that light.
He also offers some tips for purchasing the right polariser for your needs, as they come in different sizes and work in certain ways -- for instance, linear and circular polarisers.