In this chapter we shall examine the major quantities of interest in electrical systems and describe their relationships. These include voltage, current, power, energy and resistance. We begin with basic definitions and proceed to example computations. We shall go beyond the theoretical and investigate practical aspects as found in electrical laboratories. This includes measurement devices and power sources, as well as various resistive devices. We shall examine batteries from a functional perspective, and perform computations regarding efficiency and cost of energy. We will also introduce some of the device symbols used to create electrical circuit schematics. This material presents the foundation upon which we will build circuit analysis techniques in subsequent chapters. Treat it accordingly.