The Internet's backbone is an interconnected series of wide-area networks (WANs). These are large computers linked together over a long distance via phone or wireless communication. These huge WANs link tens of thousands of smaller WANs and local-area networks (LANs, computers linked together in a central location, such as a business or government organization) around the world. In this sense, the Internet IS a network of computers. It just isn't a directly connected network; it's more roundabout, more of a simulation of a network.
When you access the Internet, you can send email to anyone else in any part of the world, provided they have an Internet connection. You can download (receive) and upload (send) files and programs to and from any computer that's connected to the Internet. You can chat with other people who are currently connected to the Internet (you type what you want to say, they'll see it on their screen, and vice versa).
It's just like you're on a network of computers in a single office, for example, but the computers are spread apart worldwide.
You aren't accessing the other computers directly; you only access the single computer you're dialing into for Internet access. That computer processes your request (say, an email message you're sending), looks up the "address" of the computer you're sending it to, then "routes" your message through the necessary series of other computers out there in the network, until your email gets to its destination.
A common question is: where did the Internet come from? Most people had never heard of the Internet before that last year or two. The Internet, though, has been around for quite some time, just not in the general usage we see today.
Today's Internet that is linking people from different cultures worldwide ironically got...