Could you give more information on what you are asking about. A flash is a sharp pinpoint light source ( generally) unless modified by a softbox, umbrella, etc.

It has a "hard" quality of light. Much like the sun. Therefore like the sun you get harsh shadows. A modified flash/strobe ( one that is softened by softbox/umbrella etc) is much like an overcast day. The sun has not changed it is just diffused by the clouds, hence soft quality of light and soft shadows.

The placement of where the flash is in relationship to the subject will obviously determine how and where the shadows will appear.

I'm not sure if this is what you're looking for but if you were more specific we could answer better.

Michael MCBlane