Bracketing is often used in manual-exposure film photography, but can be a very helpful technique even with digital photography. I bracket almost all of my photographs to this day, just to have the perfect exposure.
To bracket a composed photograph, keep either your aperture or your shutter speed constant, and change the other. For example, if I were to bracket my shutter speed using a shutter speed of 1/125, and an aperture of f/5.6, I would take a photograph with these settings, then I would keep my aperture at f/5.6 and move my shutter speed to 1/250 to take a photograph, then I would move it again to 1/60. If I wanted to bracket my aperture using the former settings, I would keep my shutter speed at 1/125, and move my aperture from f/5.6 to f/8, then down to f/4.
Both of the former techniques are proper bracketing, and both of them will yield a less-exposed shot, and a more-exposed shot than the original. The original middle-ground photograph may still be better than the higher-bracketed or lower-bracketed photograph, but it's still always nice to have options for your final images.
To bracket a composed photograph, keep either your aperture or your shutter speed constant, and change the other. For example, if I were to bracket my shutter speed using a shutter speed of 1/125, and an aperture of f/5.6, I would take a photograph with these settings, then I would keep my aperture at f/5.6 and move my shutter speed to 1/250 to take a photograph, then I would move it again to 1/60. If I wanted to bracket my aperture using the former settings, I would keep my shutter speed at 1/125, and move my aperture from f/5.6 to f/8, then down to f/4.
Both of the former techniques are proper bracketing, and both of them will yield a less-exposed shot, and a more-exposed shot than the original. The original middle-ground photograph may still be better than the higher-bracketed or lower-bracketed photograph, but it's still always nice to have options for your final images.