i want to learn shadow,how to train it: )
The best way to learn light and shadow for me was to draw an egg (some people draw apples but any simple shape will do) every day with the light coming from different angles. Start with 2 values, dark and light then progress to the traditional 5 value system (form, core and cast shadows, reflected light, and highlights. Search "5 value drawing" to get the definition of these terms.
When you are confident you can then move on to the figure. Reduce the figure to basic shapes such as cubes or cylinders and play with the light. I used a small drawing mannequin for this purpose.