The internet is a collection of computers, that are connected to each other in some way or another.
Each of these computers has an address, called IP address, just like a house has a street address.
The computers on the internet that can be accessed from other computers are called servers. Not every computer on the internet is a server and can be accessed.
Computers on the internet can exchange messages and information with each other with the aid of requests that are sent over the connections of the internet.
These requests are made using the HTTP protocol. Basically that's just a common language to send messages to each other so everybody understands. At least the computers...
The message that we associate most often with the internet is a message containing a website or in other words, a HTML document. This is the essence of this book. This book contains basically everything that your computer receives when you make a request to an IP address in the internet.
Before looking further into what a website actually is i want you to know a few terms that you might have heard about before.