The Internet is a networking infrastructure, which connects together millions of computers worldwide. The name comes from the idea of "Interconnected networks".
Every computer that is connected to the Internet is part of a network, and the Internet
is a global collection of networks, big and small, linked together in many different ways

EVERY COMPUTER IS PART OF A NETWORK?

When you use a modem and dial a local number you connect to an Internet Service Provider (ISP). At work, you may be part of a local area network (LAN), which may still connect to the Internet using an ISP that your company has contracted with. When you connect to an ISP, you become part of their network. The ISP may then connect to a larger network and become part of that network.

As long as they are both connected to the Internet, any computer can communicate with any other one. "Being connected" is not only a question of cables: to be able to talk to each other computers have to speak the same language, i.e. use the same protocol. The common protocol for the Internet is called the Transmission Control Protocol / Internet Protocol or TCP/IP.

WHAT IS A PROTOCOL?

A format for transmitting data between two devices. The protocol determines, for instance, the type of error checking to be used, the data compression method (if any), how the sending device will indicate that it has finished sending a message and how the receiving device will indicate that it has received a message.

The World Wide Web, or simply the Web, is an information-sharing service built on top of the Internet. The shared documents are written in a language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. On the Web, to jump from one document to another you simply click on "hot spots" and you access the corresponding information transparently, regardless of its location. The Web uses the protocol called HTTP (HyperText Transfer Protocol).

The Web is just one of the ways that information can be disseminated over the Internet. The Internet (not the Web!) is also used for e-mail (SMTP protocol), for file transfer (FTP), and so on.