The most common response to this question is the World Wide Web (WWW), e-mail or even chat rooms. But really these are all services on the Internet. The Internet is actually millions of computers connected together in some way (phone lines, Ethernet, ISDN) so that they can share information. The Internet is really one big network of computers. All of the things that people think of when they hear about the Internet, such as email the World Wide Web, File Transfer Protocol, etc. are types of information that are shared by computers on the Internet.
The Internet is really one big network, so it is really important to understand what a network is. A network can be as simple as two computers connected to each other or it can be as complex as millions of computers connected to each other like the Internet. In order for a computer to be a part of a network it has to be connected to another computer that is a part of a network and they both have to be turned on. This allows computers to "talk" to each other. They can share files and other information. This is why your e-mail, the World Wide Web and other services on the Internet work.
The Internet is simply millions of computers networked together. It gets a little complicated, however when a lot of computers try to talk to each other. To solve this problem each computer on the Internet has an address. This address called an Internet Protocol address (IP address), allows one computer to talk to another computer across the world. An IP address contains two important pieces of information: Where the computer is located and what kind of network it is on. When a computer wants to send information to another computer it puts a label on the message which contains the IP address of the computer that the information is intended for. The information then gets passed through a chain of computers on the Internet. When a computer receives a packet of information it looks at the label and sends it in the direction of where the IP address is located. The information eventually makes its way to the computer with the correct IP address.
It doesn't really matter how far apart two computers are. As long as they are both connected to the same network, they can share information.
There are all kinds of different computers on the Internet, everything from an old IBM 286 to brand new Pentium 2 machines. Personal computers, however, only consist of one part of the Internet. There are also other machines called routers and servers.
Routers help personal computers talk to each other. They are equivalent to a tour guide or a store that sells maps. When a computer receives a packet of information and isn't sure where to send it, it will send it to its router. Routers are usually pretty smart and know where the packet should go.
Servers, on the other hand, are machines that make information available to other people on the Internet. They are primarily machines that store information like e-mail, web pages and databases. Like routers, servers are usually always on so that you can access the information at any time. In order for a web page to be visible to others on the Internet it must be put on a server.
There are a number of services on the Internet that make it easier for computers to share information. The fastest growing one is the World Wide Web. It is also the newest one. The reason why it is becoming so popular so fast is because it allows pictures, text, animation, movies, games and a number of other types of information to be shared between computers. Before the World Wide Web the Internet was much harder to use and it wasn't nearly as exciting. All of the information used to be limited to text, but now we have Javascript, shockwave, Java, CGI programming and a number of other fun tools that allow us to make exciting web pages.
Some other Internet services are: