Here's the monochrome filter effect menu in a Canon 7D. Your choices and navigation may be different but most digital camera these days have some variation of this kind of menu.
Many latest-generation digital cameras offer creative filters and the ability to fine-tune your black-and-white image-capture settings to emulate the effect you'd get if you used a color filter, or different grades of contrast paper in a traditional darkroom. Using these settings can save you several steps in post-processing so you can get the image you want straight out of camera.
The many flavors of monochrome
Why not simply shoot in color and convert to black-and-white in Photoshop? Simplicity! If you can get a killer black-and-white shot straight out of the camera with little or no post-processing needed, that saves time so you can go back out there and keep shooting.
A learning tool
In-camera black-and-white shooting can be a powerful learning tool. The instant feedback provided by the LCD preview images can help you "think" in black-and-white and quickly learn through experience how the monochromatic image transforms the nature of a composition. When you set your camera to Monochrome, the Live View in the monitor will show you the scene in black and white before you've shot it, helping you think in relative tonalities as well as compositionally.
Finally, shooting in black-and-white is a way to get out of a bad habit that's become widespread among digital photographers. Too many (myself included) rely on the abilities of Photoshop to save a picture after the fact. But if your original is accurately exposed, post-processing can be kept to a minimum.
In the physical world, black-and-white contrast filters are colored filters used to control the relative contrast between different colored elements within the frame when shot in black-and-white. Many digital cameras can emulate this effect. Let's take a look at a scene with many colors—most primary, to emphasize the differences—and see exactly how color contrast-control filters work.
The images below were done digitally using the monochrome settings on mid-range Canon DSLR. Your camera's interface and choices may vary. Check your manual to see how to access your camera's black-and-white options.