Art isn't just about self expression, art images actually fulfill a function.
Personal: Art created in order to express and share ideas and feelings
Social: Art created to represent and enforce a shared sense of family, community, or civilization.
Physical: Art created to design functional art objects.
Spiritual: Art created to represent and reinforce the shared beliefs of an individual or group.
Educational: Art created to teach or tell stories
Understanding art takes the ability to perceive. To perceive, one must use their senses and knowledge to understand that piece of artwork.