Internet & How the Web Works

When you open a website, it may look like a single page on your screen. Internally, however, many systems cooperate to produce that page.

Your device runs a browser. The browser communicates with remote systems through the Internet. A domain name is resolved to an IP address. The browser sends requests to a server. The server sends responses containing resources such as HTML, CSS, JavaScript, images and other data.

Understanding this complete chain will make later MERN topics much easier. When you eventually learn Express, REST APIs, React and MongoDB, you will already understand where each technology fits.

The Internet is the global network infrastructure that allows computers and devices to communicate with each other.

The World Wide Web is one service that operates on top of that infrastructure. Websites and web applications use technologies such as URLs, HTTP, HTML, CSS and JavaScript to operate on the Web.

Other services can also use the Internet. Email, online gaming, file transfer and many other systems are not simply the World Wide Web.

A client is the system that requests a resource or service. In normal web browsing, the browser is the client.

A server is a system that receives requests, processes them and sends responses.

The client and server can be physically far apart. They communicate through networks using defined protocols.

A browser understands web technologies and provides the environment in which web pages execute.

It sends network requests, receives resources, parses HTML, builds the DOM, applies CSS, executes JavaScript and displays the resulting interface.

Browsers also provide developer tools that allow developers to inspect HTML, CSS, JavaScript, network requests, storage and runtime problems.

A web server may receive an HTTP request and return an HTML page, an image, a JavaScript file or other resource.

In modern applications, the server may also execute application logic, authenticate users, validate data, communicate with databases and return JSON responses.

A production application may use several different servers or services rather than one physical machine.

An IP address identifies a network interface in an IP network.

Humans generally prefer names such as codebhavya.com rather than remembering numerical network addresses.

DNS provides the naming system that helps map domain names to IP addresses.

Instead of asking users to remember an IP address, websites can use domain names.

A domain can have different components, such as a subdomain and registered domain name.

The browser uses DNS to discover the network information needed to communicate with the appropriate server.

Suppose you enter codebhavya.com into your browser. Your browser cannot send an HTTP request to a name alone; it needs network information such as an IP address.

DNS allows the domain name to be resolved through the DNS system.

The complete DNS process can involve browser caches, operating-system caches, recursive resolvers and authoritative DNS infrastructure.

An IP address helps identify a network endpoint, while a port identifies a service endpoint on that host.

Common web-related ports include 80 for HTTP and 443 for HTTPS.

Developers also frequently run local applications on ports such as 3000, 5000, 5173 or 8000.

At a beginner level, think of network communication as data being carried across a network through packets.

Packets contain information needed for delivery and are processed by networking equipment and protocols.

You do not need to become a network engineer to learn MERN, but understanding that your HTTP communication travels through networking layers helps explain latency, failures and debugging.

A protocol defines how systems communicate and interpret information.

In web development, HTTP is one of the most important application-layer protocols.

Other protocols and technologies operate at different layers of the networking stack.

HTTP uses a request-response model. The client sends a request and the server sends a response.

HTTP is used not only for HTML pages but also for images, scripts, APIs and other resources.

Modern applications use HTTP extensively for communication between browsers, backend servers and APIs.

Headers become extremely important later in MERN development.

Authentication information, content types, caching instructions and many other behaviours are communicated through headers.

HTTPS provides cryptographic protection for communication between a client and server.

This helps protect data from being read or modified by unauthorized parties while it travels across the network.

HTTPS is essential for modern production websites and applications.

The browser requests the initial document.

The returned HTML is parsed into a DOM tree.

The browser discovers additional resources such as stylesheets, scripts and images and may request them.

CSS is processed to determine presentation and layout.

JavaScript may execute and change the document or request additional data.

The browser then presents the resulting page to the user.

A browser should not normally be responsible for directly storing and managing the application's central database.

The backend communicates with the database and applies rules before returning data to the client.

In MERN, MongoDB is the database layer, while Node.js and Express commonly provide the backend layer.

In MERN applications, a backend API commonly exposes HTTP endpoints that a React frontend can call.

The frontend does not need to know how the database works internally. It communicates with the backend through the API contract.

Later you will build these APIs yourself with Node.js and Express.

A browser can store cookies associated with websites.

Cookies can participate in authentication and session mechanisms.

Later in the MERN course we will study authentication, JWTs, cookies and sessions properly. For now, remember that HTTP requests do not automatically carry all application state from one request to the next.

Caching can reduce repeated downloads and improve performance.

HTTP provides mechanisms that allow clients and servers to communicate caching behaviour through headers.

Caching becomes particularly important when building production web applications.

A CDN distributes or caches content across geographically distributed infrastructure.

A user may receive static resources from a nearby edge location rather than always retrieving them from one origin server.

You do not need to master CDN architecture yet, but you should know why production systems use it.

This is the foundation for the entire MERN course.

React will eventually control the frontend interface.

Node.js will provide the JavaScript runtime on the server.

Express will help build HTTP APIs.

MongoDB will store application data.

The browser and backend will communicate primarily through HTTP.