This theory attempts to provide a unified model of the mind, similar in scope to Newell's Unified Theory of Cognition, but with the premise that the mind's individual components lend little light on the mind as a whole; that it is only when connected and interacting that their purpose becomes clear. These agents can then be organized into various heterarchical or hierarchical structures, with those agents at the top commanding (i.e., turning on and off) those below, those at the bottom often muscle-motor agents. Interaction between agents can range from simple switching, or to conflict between two for solution to a goal, etc.
This excerpt from The Society of Mind sums very well the point of Minsky's book:
The power of intelligence stems from our vast diversity, not from any single, perfect principle. Eventually, very few of our actions and decisions come to depend on any single mechanism. Instead, they emerge from conflicts and negotiations among societies of processes that constantly challenge one another. --Chapter 30.8, page 308.