When an object or a shape occupied certain space, we call that space is positive space. Whatever space is not occupied by a shape on the picture plane that is negative space. These positive and negative spaces are very powerful tools to understand the size and proportion of the shapes. Taking these shapes, making them as forms through creating volume, placing them in spatial arrangement is a part of creating depth on picture space.
(Studying Composition means Learning Painting. There are no other ways to learn painting than understanding composition. I have come to a conclusion that it can be explained through 200 compositional studies. I am planning to post 200 composition studies in the next 300 days)