Quick and simple answer to : What is a LAN (Local Area Network) versus a WAN (Wide Area Network)
In a typical LAN (Local Area Network) a group of computers and devices are connected together by a switch, or stack of switches, using a private addressing scheme as defined by the TCP/IP protocol.
Private addresses are unique in relation to other computers on the local network. Routers are found at the boundary of a LAN, connecting them to the larger WAN.
In a WAN (Wide Area Network) you will have multiple LANs connected together using routers. I was taught many years ago that a WAN had nothing to do with the size of a computer network, but was simply connecting multiple LANs together across the public highway system, such as the internet.
If you have a three computer LAN than uses the public highway, as in the internet and internet addressing, to connect to another three computer network, the two LANs working together form a WAN.
People often try to explain concepts like LAN and WAN using terms and descriptions that have nothing to do with the definition. I often see people put numbers of computers into their definitions of LAN and WAN. The number of computers is not significant to the definition. The physical type of connection, as in copper wires, fiber, wireless, has nothing to do with the definition.
You may not be familiar with the specific function of a network switch versus a router, or the definitions of private addressing scheme versus a public address, they are more advanced topics of computer networking, but they are the core elements that separate a LAN from a WAN.