If you struggle to understand the idea of composition in two-dimensional art, be consoled. Although composition sounds as if it ought to be systematic and simple, it's elusive and mysterious. Few artists or cognoscenti can provide a useful definition or demonstrate the principles by which it functions.
Artists often discuss composition in terms of spatial relationships.
This is also true when dealing with abstract two-dimensional works. The surface is animated with gestures that propose a relationship with a surrounding area, often conceived as a background. The argument of these relationships in one part of the work relative to another determines the composition. If the weightings seem to correspond, the composition seems to work. An example is Kathleen Mitchell at Gallery 101.