Don't get carried away with the use of flash, unless you have a very good reason. Flash completely alters the look of the light in your photo, and often does more bad than good: especially when you're drawn to the light that you're trying to photograph. Perhaps oddly, the opposite of one's normal intuition is correct when it comes to flash usage:
- flash for use outdoors in bright sunlight
- no flash for use indoors in low light
One of the most important uses of flash is fill flash: this is when you use your flash to balance out the available light. The best example of this (and the most frequent situation that one may photograph in) is when photographing someone in bright sunlight, when the sun is either behind or above the person you're photographing. The two dashing portraits of me below were taken (with my outstretched hand) with a Canon SD 1400 IS point-and-shoot camera, to demonstrate that even the smallest camera's tiniest flash can serve as a fill flash. Note how in the second shot the bright sunlight is still in the same spot as the first, but the flash lights up my face to balance the shot out.
Using Flash in Low Light
The reason that flash is not always ideal is that to light something correctly is quite complex: a built-in flash has very little functionality at all, and even an external flash has its limitations. Even the most powerful built-in flash on a DSLR is only really good for about 10 feet or so at the most. It will work very well for fill flash (above) but not for lighting anything meaningful.
The photos below illustrate three different things.
1. The flash really only is effective for about 3 feet: the only thing it lights up in the photo on the left is the back of the guy's head and some of the white shirt in front of him. Ultimately, the flash only creates a huge distraction away from the focus of the photo (the stage at Radio City Music Hall).
2. The flash doesn't change the light in the primary subject (the stage) in this instance, which as with what was stated in #1 renders it useless (and a distraction to the other people who have to deal with the backs of heads being lit up during the show). In other instances, using the flash will illuminate whatever's immediately in front of the camera, and completely blacken out anything behind it.
3. These two shots were taken with an older Canon SD 780 IS point-and-shoot, illustrating that "my camera isn't good enough" is not a valid excuse. Whatever camera you have, you can make it work!
This section on flash is short on purpose: as you move through these initial steps of learning DSLR photography, only use flash 1. if you need it for fill flash, or 2. if you have no other choice. I'll note in sections below when you might want to use your flash - if nothing else is working for the particular subject matter you're photographing.
An external flash gives you many more options, but these options will not be discussed in this introductory material.