There are many ways to create silhouettes, but one thing is for sure -- you have to turn off the flash first. If your flash pops, your subject won't be a dark shadow. After you disable the flash and before you start tinkering with your camera's manual settings, try using your auto mode.
Almost every digital camera lets you lock the exposure and focus by depressing the shutter button halfway. This is a very useful attribute for silhouettes. For example, if you point your camera at a person standing in front of a sunset, you can tilt the camera toward the top of your subject's head, lock the focus and exposure, and then recompose the picture. In doing so, you're exposing the picture more for the bright sky than the much darker subject, ensuring a nicely saturated sunset with a dark subject that's sharply focused. If you have a hard time getting the autofocus to lock onto your subject in the harsh light, switch to your camera's manual focus setting before you lock the exposure.
If the auto mode doesn't work well for your purposes, check to see if your camera has an exposure bracketing feature. Exposure bracketing tells your camera to take three pictures in quick succession at three different exposure levels. One is the camera's best guess as to an accurate exposure for every part of the composition, one is underexposed and the other is overexposed [Canon USA].
Exposure bracketing is designed to help you snag at least one usable image in a scene with very bright and dark areas. You simply shoot with this mode and then pick the exposure you think is best after you're done. Bracketing also makes it easy to capture partial silhouettes, in which you reveal a little detail in your blackened subject by choosing a brighter exposure.
Your camera's manual or shutter priority modes may also come in very handy. These modes let you control shutter speed with ease. A faster shutter speed means a shorter, darker exposure, while a longer shutter speed makes a brighter picture. So, if your subject is too dark or too light, just change the shutter speed with a quick twirl of your finger.
Now that we've tackled some of the technical aspects, head to the next page to read about general advice to keep in mind when composing silhouette photographs.