What should you silhouette? Given the right lighting conditions, you can turn almost anything into a silhouette, but not every subject will look good as a shadow. Remember that a silhouette lacks detail--it's just an outline filled in with black. Consequently, you should look for subjects with strong, recognizable shapes. A complex, busy subject might not work, especially if you need to see details to make sense of it.
You can get good results with any camera and any kind of exposure control.
First, turn off your camera's flash. We don't want to throw any light on the front of your subject.