This document provides an introduction to different types of computer networks. It defines what a computer network is and discusses the first computer network, ARPANET. It then describes the main uses of networks, including sharing resources, communication, accessing remote files, backups, and distributed computing. The document outlines four main types of networks: local area networks (LANs) which connect computers in a building or nearby area; wide area networks (WANs) which connect computers over long distances and cities; metropolitan area networks (MANs) which connect organizations within a city; and personal area networks (PANs) which connect devices within 2 meters of a person, such as phones and PDAs. Examples are provided for each type of network.