A candle snuffer is a tool made of a hinged bell attached to a handle. Its purpose is to neatly put out burning candles, without the danger or mess of spattering wax. Candle snuffers are usually made of brass, pewter, or iron, though some are made of heat-resistant resin.
The candle snuffer is a quaint implement, which harkens back to pre-industrial days when many, many candles would have been needed to adequately light a room. Blowing them all out certainly would have required a lot of breath! Also, candles in the past were often made out of animal tallow, which is messier than modern waxes. (It melts at a lower temperature, splatters more, and attracts pests--thank goodness for paraffin!)
Besides antique stores, you'll often see candle snuffers in metaphysical stores. In ritual magick, the candle snuffer serves a very specific purpose, which is to signal the end of a working. Magicians may light candles to focus energy, represent the Quarters or Elements, or signal the presence of invoked Gods or spirits. Snuffing out a candle is a great visual aid to help dismiss the power(s) represented by the burning candle.
Some magick workers are very opposed to the practice of blowing out candles with the breath. To these folks, the only proper way to extinguish a candle is to pinch or snuff it out, or to let it burn out on its own. Reasons vary, but some say that the breath "blows away" or disrupts the energy of the spell, or that to use Air to extinguish it is disrespectful to the related element of Fire. It is also considered safer (physically) to snuff a candle, rather than leaning in to blow the candle out, possibly spraying hot wax or igniting hair or clothing.
So, do you really need a candle snuffer to put out your candles? As pragmatic Witches, we're inclined to disagree with any rule that says you "can't" or "must" perform magick in a certain way. (We've been blowing out ritual candles for years without any ill effects.) If you follow common-sense fire safety, like keeping burning candles away from flammable objects, blowing out your candles should be just fine.
Still, we can't help but admit that candle snuffers have a certain old-timey charm. They're also very useful for putting out half-spent jar candles and other hard-to-reach places. If you do a lot of candle magick, a fine snuffer may be just the thing to add to your altar kit.