Though I plan on doing a series of more in-depth looks at parts of the internet, if you don't understand what the internet is at all, this is a good starting point.
The internet is a concept as much as a thing. There is no one person or entity that controls the internet. There is no one big bank of computers hold the content of the internet. There is no one company responsible for the network infrastructure that carries the data through the internet.
Instead the internet is comprised of any computer that connects to a network that connects to the "public" network that is the internet. Checking your email causes your computer to connect to a server that is connected to the internet. Searching for things on the web causes your computer to connect to servers that are connected to the internet.
A server is basically a name for a computer with a specific purpose. While virtually any computer can act as a server, in a corporate environment servers are typically very high powered computers optimized for storing, processing, and transmitting a specific type of data. A database server handles storing structured data, accessing specific portions of that data, and sending that data to other computers that request it. An email server runs software designed to accept large volumes of email destined for a specific group of people (i.e. company, internet service provider, college, etc), to hold on to that email until requested by the individual account holder. A web server holds documents and scripts that will be delivered to a person requesting them using a web browser. A single server can fulfill multiple purposes. The same computer can be a web server and an email server. By the same token, multiple servers can work together to achieve multiple purposes, or to achieve the same purpose for a large number of users. For example when you visit the home page of a very large internet search engine you may reach one of dozens or even hundreds of servers that all contain the home page of the provider, thus distributing the work to improve performance. And that one web server may retrieve your search results from one of dozens of database servers that keep the search data.
The internet is the collection of those servers all interconnected using a structured system of addressing that permit any one computer attached to the global network to access any other computer attached to the same global network. The data can travel through multiple countries, through equipment owned by dozens of different companies, and to individuals across the world and it can do it all in a as little as a second despite not even knowing the first thing about how the data gets from one point to the other. Again, I'll discuss in more detail exactly how that works in another post, but I will give a quick outline of how it works here.
When a computer connects to the internet it is given a unique address known as an IP(internet protocol) address. The information on which computer has which IP address is kept in a server known as a DNS (domain name service) server. There is no one DNS server that keeps every single address in it, instead they each keep the data that is most pertinent to the people (companies, schools, etc) that use them the most. They also have the information about what other servers can give them addresses that they don't have. The address information that is provided helps routers (network devices that direct traffic where it needs to go) know where to send data. The data is passed through a series of routers and servers to get from point A to point B. Often, when travelling long distances it will spend time with a backbone provider, which is one of several companies that maintain data lines capable of carrying massive amounts of information. Most international communication takes place over backbones.
So in a nutshell, the internet is as much a concept as a defined object. It changes every day with servers going online, servers going offline, addresses changing, data lines being damaged, new data lines being installed. The result is a "grid" that allows for redundancy in the case of a failure of a portion of the grid. And one important distinction to keep in mind is that the internet is not the same thing as the web. The Web or "World Wide Web" is simply one portion of the activity that takes place on the internet.
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