There are three main types of computer networks: local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). LANs connect computers within a small area like a building using technologies like Ethernet. MANs connect multiple LANs within a larger area like a city using technologies like Frame Relay. WANs connect LANs and MANs across large geographic areas like countries using technologies like the Internet. Each network type increases in size and geographic reach but decreases in connection speed.