There are basically two types of shadows. The shape cast by the light and the shading on the object.
Light produces shadow, and the source of that light is important to the painter. The type of shadow is influenced by the light source, which can be high, low, to one side, in front or behind.
The intensity of the light source will affect the tonality of both shading and shadow, and its proximity to the object will affect the intensity of the shadow.
The sun causes many objects to have shadows and at certain times of the day, when the sun is at certain heights, the lengths of shadows change.
If there are multiple light sources there are multiple shadows, with overlapping parts darker, or a combination of colours.