Black and white photography is the original; classic, striking, moody, and reduces the photo to a more fundamental state. It is one of my favorite forms of photography and from some of the most famous photographers, there is nothing quite like it. Ansel Adams, Mary Ellen Mark, Yusuf Karsh, amount many others, are renown for their use of black and white.
In today's digital world, there are very few actual black and white cameras; the Leica Monochrom, Red Epic-M Dragon (monochrome) are a few notable examples that come to mind but, generally, if you're using a digital camera, even with a black and white mode, you're shooting color (RGB — red, green, blue) and it is converted to black and white. In other words, if you're making or seeing black and white digital photography, chances are you're look it was originally color.
Without giving a long scientific explanation of why or how digital cameras work, a "general" digital camera have a sensor with pixels, each capturing its own color: red, green, or blue. The Leica M Monochrom uses a sensor where each pixel captures only luminance.
Many of us simply can't afford a Leica or we would really like the option of color photography. Sadly, we can't, or currently can't, have a camera that is "dual-action" color or mono. As such, we'll need to settle for one or the other but don't be discouraged, a color photo can be altered into a stunning black and white photography.
In OS X's Photos app, there are three filters for use to convert your images: Mono, Tonal, and Noir (my personal favorite). Having covered how to use filters in a previous post, we'll forego these and move into a more advanced technique for black and white conversions and more flexible.