A router is a switching box programmed to send data where it needs to go. Large routers connect networks over the Internet. Small routers connect computers and other devices on a home or office network, also called a Local Area Network (LAN).
If local area networks (LANs) were like plumbing, then Ethernet cables would be the pipes and routers the valve switchers. But data bits have a huge advantage over fluids. They don't require conduits to flow through your home or office to still be useful.