A computer network is when two or more computers or devices are connected to one another either via Ethernet wires or wirelessly. This could be a computer connected to a wireless printer or one computer connected to another. However, connecting a printer directly to a computer without the use of Ethernet or over Wi-Fi, such as using a USB connection, does not count as a network as it is not using a network connection. This is why a USB thumb drive connected to a computer also doesn’t count as a network device. Network-attached devices are able to send and receive messages from one another through the network connection, such as; emails, files, notifications, etc.
When devices are connected to a network they can send messages back and forth, and there are different types of messages that can be sent. Each type of message has different protocols, which are like rules, that define how the messages should be structured and the contents of those messages. Think of the difference between sending an email and sending print job request, they will contain different things and look different.
Networks can span different physical locations or be within one location. A LAN or Local Area Network is a small network that usually exists within one physical location such as a home or an office. A WAN or Wide Area Network is a large network that isn’t restricted by geographical location and generally connects multiple LANs together. The internet is the best example of a WAN, which is basically a global WAN made up of many LANs. However, some businesses will create private WANs to connect different offices together, again connecting multiple LANs.