Hierarchy aids in the exploration of any composition. Its helps identify which areas have greater importance over others. It helps the viewer identify which areas will likely be taken in fist, second and so on.
A focal point is the most active area in a composition. Some prefer calling it an entry point. Not every composition requires one, depending, of course on the nature of the composition and frequently if there is an idea or concept to express. (Side note: two focal points may invoke confusion or confrontation. Three focal points could make things even more chaotic. On the other hand three focal points could promote an interesting pattern, but typically among beginning students, multiple focal points contribute mightily to chaos.)
Focal points lead the viewer typically into secondary areas of interest and thus into the heart of creating hierarchy. (Hierarchy and focal point are also covered under the Active/Passive definition, listed in later exercises.)
Below are examples of hierarchal compositions and hierarchal compositions with focal points. How is the artist controlling what we see first, second and so on?