In the first chapter, an overview of the structure of the distribution system, its components, and the role of the distribution system in the larger picture of the power system is given. Then, in the following text, terms related to the quality of electricity, factors that provide insight into the quality of delivered energy and reliability of delivery are explained. Basic modeling of system components and their behavior as they age are also explained. Before the elaboration of some more complex analyzes and simulations of system behavior, the basic terms related to these simulations and analyzes are explained in order to enable a clear understanding, and the frameworks and principles of modern methods and analysis of distribution systems are given.