Of course, the real world of economics is very complex. The allocation of resources in a market economy is the result of the interaction of thousands of decisions made by each of hundreds of millions of individual people.
Dynamics is the way the subsystem evolves as time passes.
Models are usually somewhat more complex than theories, and a theory may be just one part of a model. Like theories, however, models are abstract, and must ignore some aspects of the system they describe. In economics, a model is most likely to take the form of a list of variables and one or more relationships among the variables. These variables and relationships describe the interdependence among the people and activities in the economic system or subsystem, and the way these activities change as time passes. Examples serve best to make this clear.