Unlike color images, black and white is all about controlling contrast.
Most people find making b&w images much more difficult than working in color.
Desaturating (removing the color) an image can be done in a lot of different software. Channel Mixer and Adjustment layers are Adobe Photoshop features for converting color images to black and white. Contrast in a b&w image can be controlled to a surprising degree by altering how much saturation there is of a specific color. Increasing the blue saturation will make the sky darker on the b&w layer.
In the days of b&w film photographers used colored filters on the camera lens, and/or the enlarger lens to manipulate contrast.
One of the best known b&W photgraphers of the last century, Ansel Adams, was not so much a brilliant photographer as he was brilliant in the dark room processsing the negative into prints.