My first attempt at understanding tonal differences was quite intimidating. What your mind perceives and your eyes absorb, may not translate the same on paper. But over a period of a month now, I have been able to better appreciate subtlety and the nuances in applying the various tones moving from light to dark.
In drawing and shading, you have only two colours, black and white. It is simply a question of applying the right pressure to bring out the different tones - but it is not quite that simple.