Packet Switched Networks break data down into smaller components called network packets, prior to transmitting the data over a network. The internet is a PSN that uses TCP/IP to transmit data. TCP breaks the data down into smaller pieces (network packets) to improve transmission efficiency. Then, IP routes the data using an IP address.
This packet switched network allows multiple devices to utilize the same network.
Routers are the bridge between networks because they receive and transmit network packets. When a router receives a network packet, it figures out where the data should go and then sends it there.
Network switches connect devices within the same network. Large businesses often have a separate switch, but most household internet setups use a router with a built-in Ethernet switch. Ethernet is the most common way devices are connected together on a LAN (Local Area Network).