Black and white photography is completely dependent upon tone. Tone is the various amounts of light and dark in a photo. More contrast means more tones. Color photographs also have tone but also have an extra element of hues. Below are a few examples of tone in black and white photography.
This macro photograph of a blooming flower uses tone to separate the background from the foreground subject. Tone also gives detail to the leaves.
Tone also separates the background and foreground in this image. There isn’t much light tone in the gorillas so it is nearly a silhouette.
The clouds made this photo front the summit of Tusquitee Bald. The clouds had so much variety of tone and the shadows cast on the ground added to the contrast in the mountains.
This shot of a sunset uses tone in small detailed areas to give it a high contrast look.
The last shot is a macro image of a cluster of flowers. These flowers were a bright purple, but adding a black and white filter in post processing added a huge amount of contrast.
Check out some of my outdoor photos at Sizemore Outdoors.