I've talked about the AV setting, the TV setting and the ISO of the camera. These settings are the base for understanding the bulb setting. The bulb setting, the "B" on your cameras dial allows you to set the AV setting and keeps the f-stop open all the way. The biggest use of this setting is for photographing at night.
Here's what happens, turn the cameras dial to B. You'll see the display says "bulb" and you can decide how small or large the aperture is. When you push the trigger the lens will stay open as long as you hold the button.
While I was making sure I was giving the correct information, I found out that my camera displays a count of the seconds I've held the trigger open. At first i thought that was as good as sliced bread, till I remembered in the dark you cant see it counting. I'd have to shine a light on the display to see how long it had been and that could mess up the photo.
Back when i was using a film camera for everything I had the timing down to a science. I knew how long any given photo would take to get it right. For a few years when i had a digital camera I still liked the film for my night shots cause I knew how to work it. Now that I've figured out the digital I've relaxed on knowing how much time each photo needs. Now the way i keep track of the time is by either counting or simply guessing. Before I leave a shoot I have checked my images to be sure I got what I wanted.
It is a lot of fun to go out and use the bulb setting. For me it helped me really understand my camera. Now it's your turn, get out there and have sime fun.