Usually when people think of silhouettes they think of sunsets. But a silhouette happens any time you have a contrasty situation and the foreground object is in shade and the background object is in bright sunlight.
The reason you get a silhouette is because of the inability of film (and digital) to show details in both the highlights and the shadows at the same time. When I looked at this scene with my eyes I could see detail in all of the foreground landscape.
The trick to getting a good silhouette is to be careful of where you take an exposure reading from. In this particular image if I had taken an exposure reading from the foreground, it would have been well exposed while the background mountain would have been totally white and burnt out.
So the trick is to take an exposure lock of a nice grey part of the mountain in the background or that lovely blue sky (which is roughly 18% grey). That will send your foreground nice and dark.
Keep an eye on your histogram and see how dark those silhouettes really are. If your histogram is still quite a way to the right hand side you might need to darken things a bit so dial in a bit of exposure compensation (the one with the +/- on it) until your histogram moves back to the left.
This picture was taken in the high Himalayas of Nepal. We were in the little town of Namche and this shot was taken with a 400mm lens with a 1.4x converter on it. I used quite a small aperture to get as much depth of field as possible with such a long lens.