Imagine you have to send a large photo to a friend. There are two basic ways a network could do it.

Circuit switching is how old telephone networks worked. When you call, the network reserves a whole line from you to the other person for the entire call. Nobody else can use that line, even in the pauses when nobody is talking.

Packet switching is how the Internet works. The message is cut into many small pieces called packets. Each packet is sent on its own, and the network shares its links between everybody's packets. Packets from many different conversations take turns on the same wire.