If you're wondering what it does and how it works, let me quickly explain it all for you. Basically, a fireplace blower will take the warm air from the fireplace and it blows it across the room. It's just like a fan, but it blows the hot air instead of cooling it. This spreads the warmth around and I no longer have to sit a few feet away from the fireplace to feel its effects.
Taking measurements of your fireplace is one task you should perform before researching the costs and types of fireplace blowers available, if you are planning to affix it to your fireplace. If you are uncertain of which type or style to purchase, then determine what your specific needs are for the blower. Once you have an idea of what you want to use it for, then you should be able to ask the right questions of the retailer or store proprietor.