[alan1]

what is the bulb switch on the camera for and how is it used?

[montezuma]

The bulb switch is a special shutter speed mode allowing for long exposures. Normally, the camera body only allows you to go up to a 30s exposure, in bulb mode the shutter will stay open as long as you hold down the shutter button. This mode is good for night photography, astrophotography, or anything that may need exposures longer than 30s. For bulb to be useful a tripod is needed and a wired remote shutter is strongly recommended to reduce camera shake and it has a lock button feature that allows you to take your hands off the shutter button for very long exposures. If you've ever seen star pictures with trailing stars, or trailing car tail-lights this is how they get that effect: by leaving the shutter open for long periods of time the sensor captures the light as it moves through the frame leaving trails of light behind. If you don't do star shots, or night photography bulb mode isn't too useful, at least in my opinion.

[rbefly]

Hello Alan1, Welcome to the Forum!
As Montezuma said, "B" (Bulb) mode is for long shutter exposures.
Another use I've found for B is shooting fireworks. Although you can set a (typical) firework display shot at anywhere from 3-6 seconds with an aperture of f/5.6-f/8.0 and ISO 100, there are a couple of variables that come into play.
First, the initial displays may start before it's full dark. These will usually need a shorter exposure, 2-3 seconds. Later, when the sunset is gone, the exposure will be 4,5, up to 6 seconds.
Second, you may have set a short exposure and another rocket explodes just as you're at the (timed) close of the shutter. If you could leave the shutter open for another 1 second, you could catch 2 bursts in the same frame without ruining the shot. The difference between 3 and 4 seconds usually isn't enough to overexpose the photo.
In both instances you're better of using Bulb and the old reliable "One thousand one, two thousand two," etc.
I use Bulb for all types of night shooting, starting with (a countdown of) 3 seconds at f/5.6, then 4 seconds, and so on. When I find a time that works, I set it into the camera and (assuming the light stays the same) use the camera timing for the rest of the shots.
It seems easier to use this method, considering the fact that you're working in the dark!
JMO,
Ron