This document provides an introduction to computer networks. It defines what a computer network is and describes different types of network topologies including bus, star, tree, ring and mesh. It also discusses different components of a computer network such as physical media, networking devices, computers that can serve as clients or servers, and networking protocols like TCP/IP. Finally, it lists several applications that are commonly used over computer networks like email, websites, e-commerce, VoIP and video conferencing.