Although they look similar, modems and routers perform different functions to connect you to the Internet. A modem is a device that provides access to the Internet while a router is a small box which allows multiple computers to join the same network.
Your modem communicates with your provider’s network, transmitting and receiving the data over the line. A router on the other hand directs data in a network, passing data between your computers and the modem. A typical router creates hosts a Wi-Fi network that multiple devices can connect to. It often has multiple Ethernet ports as well, allowing you to connect multiple devices with wired connection.
Some modems double as routers, like the modems we send out for VDSL connections. For our fibre connections, we provide a router since the ONT (Optical Network Terminal), the internal connection point for fibre, is a type of modem which our router would then plug into.