A computer network is a group of devices connected with each other through a transmission medium such as wires, cables etc. These devices can be computers, printers, scanners, Fax machines etc.
The purpose of having computer network is to send and receive data stored in other devices over the network. These devices are often referred as nodes.
There are five basic components of a computer network
Message: It is the data or information which needs to be transferred from one device to another device over a computer network.
Sender: Sender is the device that has the data and needs to send the data to other device connected to the network.
Receiver: A receiver is the device which is expecting the data from other device on the network.
Transmission media: In order to transfer data from one device to another device we need a transmission media such as wires, cables, radio waves etc.
Protocol: A protocol is a set of rules that are agreed by both sender and receiver, without a protocol two devices can be connected to each other but they cannot communicate. In order to establish a reliable communication or data sharing between two different devices we need set of rules that are called protocol. For example, http and https are the two protocols used by web browsers to get and post the data to internet, similarly smtp protocol is used by email services connected to the internet.