You can say Internet is a worldwide network of computer networks.
The Internet evolved from the first computer network named ARPAnet.
The Internet is made up of too many networks. Each network run by a different company and all are interconneted at peering points.
You can also say that the Internet is an interconnection of both large and small networks around the globe.
The Internet connects many smaller networks together and allows all the computers to exchange their information with each other. To accomplish this all the computers on the Internet have to use a common set of rules for communication. Those rules are also called as protocols, and the Internet uses a set of protocols called TCP/IP stands for Transmission Control Protocol/Internet Protocol.
The general use of the Internet is, users connected to one network to communicate with users on another network.
In Internet, most computers are not directly connected to the Internet. Rather they are connected to the smaller networks, which in turn are connected through gateways to the Internet backbone. Here, a gateway is a device used to connect dissimilar networks. And, a backbone is central interconnecting structure used to connect one or more networks just like the spine of a human being.
Here are some steps shows how Internet functions: