This document discusses virtualizing networks using VirtualBox and Leonidas virtual machines. It provides instructions on downloading VirtualBox, copying the Leonidas virtual drive image, and installing necessary software onto a master Leonidas image that can then be cloned to create duplicate virtual machines easily. Various terms related to virtualization and virtual machines are defined. Potential practical applications of virtual machines like learning Linux, security testing, and networking are described. The document demonstrates configuring internal networking between cloned virtual machines in VirtualBox.