In order to understand the difference, you should first know what LAN and WAN mean. When you say LAN, this means Local Area Network. This is usually composed of different computers and other network devices that are connected to just one computer.
This can usually be placed in one building, and all of the devices that are under one building will be using the LAN. The WAN is known to be a type of computer network that would connect the different LANs.
This can be used when you know that there are various areas that would need to be connected to each other, even when they are located in varying buildings.