This chapter aims to guide readers in understanding social networks and their computing methods through the five key questions of “4W1H.” These questions correspond to the context of social networks, the subjects of social networks, the definition of social networks, the types of social networks, and the calculation of social networks. This chapter begins by introducing the concept and basic forms of social networks, such as inter-individual networks, organizational social networks, and diffusion networks (both online and offline). It then explores how social networks are represented in computers, the methods of calculating them, and their practical implementation. Through these discussions, this chapter provides a theoretical framework for understanding complex social phenomena in the Internet age and lays the foundation for the application of social network computing in this chapters that follow.