In this chapter, we present a comprehensive introduction of the ComNets Emulator (ComNetsEmu), which is used as the lightweight Free and Open-Source Software (FOSS) test bed for all practical examples of innovations and technologies described in this book. ComNetsEmu emulates a real-world deployment and orchestration of containerized applications running on clusters of physical servers on a single laptop. Initially, we analyze the limitations of the original Mininet network system emulator followed by the motivation to extend it to a holistic test bed for network softwarization. In this chapter, we describe how lightweight, user-friendly approaches and simplified Docker-in-Docker technology are employed by ComNetsEmu to achieve this goal. Furthermore, in this chapter, we introduce the reader to working with ComNetsEmu, from initial deployment to working with the emulator.