They key to how the Internet works is understanding what the Internet is: The Internet is actually a network of networks. It cant easily be defined as a single object, or run by just one computer or company. The Internet is basically the network of the world. Anything you can get off of the Internet from your home you can get it from any computer on the Internet around the world, countries like China and Japan.
The Internet is the worlds largest distributed system; it was designed and engineered with an abundance of routes, connections and easily recovers from a mishap. The Internet is not a single company or group of companies, and it's not even a singe network. It is a worldwide mesh or "matrix" of hundreds of thousands of people in hundreds of countries, all interconnected by "ICP's". Not a single organization controls the internet; not the U.N.
or the biggest "ISP's" such as America Online. Since the start of the Internet it has outgrown control by the U.S government. The Internet is different from other major services. Electricity tends to be provided by a single company in each geographical area. The "last mile" of telephone service to the customer is usually owned by a single company. But in general there is more than one Internet provider, and there are usually many paths from a local provider in one area to a provider in another area. There are many different ways to connect to the Internet. A couple examples are either by a telephone line, or by a cable connection. The different connections all have different speed in which they connect. The cable connection is much faster then the telephone connection.
The internet is capable of many things, it can send pictures or letter, or...