Hi Yammy - I think that you will find that most artists never use black (at least in traditional paintings) because it is considered a 'dead' color. It has no life or character. The study of shadows can be quite complex, but the general theory is that they be 4 values darker than the lighted parts. (value is the relative lightness and darkness of a color using anywhere from 5 to ten different 'shades' of the same color). You would use the little vertical slider at the right of the color palette to change values. Color theory is quite complex also, but in general an outdoor scene will have shadows that are similar to the sky color. Usually blues and purples will give convincing shadows.
Hope that helps and doesn't add to confusion. Happy painting.
Give a man a fish and you feed him for a day - Teach a man to fish and he will sit in a boat and drink beer all day! Joe V.