Web

The Web has become one of the fundamental infrastructures of our everyday lives. We use it to communicate, work, study, stay informed, purchase products, watch content, use applications, and access services. Yet, precisely because it has become so familiar, we often tend to take it for granted: we open a browser, enter an address or perform a search, and a few moments later, a page appears on the screen.

Behind this apparent simplicity, however, lies a complex technological system built through the cooperation of numerous components.
When we visit a website, our device must locate a server across the network, establish communication with it, request specific resources, and receive a response. The browser must then interpret HTML documents, apply CSS rules, execute programs written in JavaScript, and integrate images, fonts, videos, and other content. During this process, cookies, sessions, and authentication systems may be used, while protocols such as HTTP and HTTP/3 govern the exchange of information.
The website we see on the screen is therefore merely the final result of a long sequence of operations.
Understanding the Web means learning to observe what happens behind that interface.

This book was written with precisely this goal in mind: to develop a comprehensive understanding of how the World Wide Web works, connecting technologies that are often studied separately.
We will begin with the general architecture of a website and the relationship between clients and servers, exploring how resources are organized and distributed across the Internet. We will then examine one of the tools we use most frequently but understand the least: the browser, focusing on its role in interpreting and displaying web pages.
Next, we will explore the structure of web documents through HTML, the language that describes content and semantic relationships within a page, and CSS, which defines its presentation, layout, and responsive behavior.

But a web page does not exist in isolation on our computer. It must be requested over the network.
For this reason, we will need to understand HTTP, the protocol that enables communication between browsers and servers, and its most recent evolution, HTTP/3, which is based on QUIC and designed to make web communications more efficient and resilient.
From a Web primarily composed of documents, we will then move on to the Web of applications.
JavaScript makes it possible to introduce logic and interaction directly into the browser, while server-side languages such as PHP allow content to be generated dynamically and web pages to be connected to databases, authentication systems, and services. Understanding the difference between client-side and server-side processing allows us to view a website not simply as a collection of pages, but as a distributed system in which different components work together.

We will also examine one of the smallest yet most important elements of web architecture: HTTP cookies. Through them, we will understand how a protocol originally designed to be stateless can support sessions, authentication, user preferences, and tracking, while also addressing some of the major issues surrounding security and privacy.

These technologies form the foundations of the Web, but in most contemporary projects they are not managed directly.
Content Management Systems (CMSs), such as WordPress, introduce an additional layer of abstraction that makes it possible to create and manage complex websites through themes, plugins, databases, and administrative interfaces. Studying a CMS after understanding the underlying technologies helps us recognize what it automates and which parts of the architecture still depend on the Web’s fundamental mechanisms.
Finally, we will analyze the role of search engines
, examining how they discover pages through crawling, organize information through indexing, and determine which content to display to users. From there, we will also be able to understand the meaning of SEO, not simply as a collection of techniques for gaining greater visibility, but as a consequence of how content, document structure, and web architecture are interpreted by search systems.

The purpose of this book, therefore, is not to turn the reader into a specialist in every technology described.
The goal is to develop a mental model of the Web.
To know what happens when we enter a URL into a browser. To understand where the content we see comes from. To distinguish what is processed by the browser from what is processed by the server. To understand why HTML, CSS, and JavaScript exist and what roles they play. To interpret an HTTP request, understand the purpose of a cookie, recognize what a CMS automates, and grasp how a search engine manages to find a page among billions of documents.
Because using the Web is simple.
Understanding the Web means learning to see the invisible infrastructure that makes that simplicity possible.