Web Technology

The browser request starts with a URL going to a DNS server to resolve an IP address; the browser then connects to that address, and the web server sends back the requested page. All of this rides on TCP/IP — TCP breaks data into packets, IP routes them to their destination.
Two kinds of communication happen on the web: client-to-server and server-to-server.

Plain browsing needs no authentication, but anything sensitive — banking logins, payments — is encrypted with HTTPS, which layers SSL (Secure Sockets Layer) on top of HTTP. The server presents an SSL certificate, the browser verifies it with a certification authority, and only then does the encrypted session begin.
Server-to-server communication (e.g. a shopping site talking to a bank) works similarly, often routed through a payment gateway that bridges merchant and bank servers securely.

A web server is both a powerful, always-on computer and the software installed on it (Apache, IIS, nginx, GWS) that delivers pages on request over HTTP. These machines usually placed in a data center — having the facilities like backup power, cooling, and high-speed networking.

Every service on a server is reached through a numbered software port

A DNS server resolves a domain name to an IP address, checking first the browser's own cache, then the OS cache, then the ISP's DNS, and finally a recursive search starting from one of the 13 global root servers if nowhere else has the answer.

Beyond a plain text editor, dedicated tools like Bluefish, Dreamweaver, and Adobe/Microsoft Expression Web let designers build and link pages visually, and often bundle in FTP upload for publishing directly to a server.

A script is program code embedded in a page via <SCRIPT>.
Scripts are of two kinds:
client-side (JavaScript, VBScript) runs in the browser.
server-side (PHP, ASP, JSP) runs on the server and returns plain HTML.

Ajax fetch data in the background without a full reload.

CSS separates a page's content (HTML) from its presentation (colours, fonts, spacing, layout). It can be applied three ways: inline (a style attribute on one tag), embedded (inside <HEAD>), or linked (an external .css file) — linked CSS is the most reusable, since editing one file restyles every page that links to it.

Every HTML file is built from tags (the commands) and attributes (extra parameters on a tag).
Container tags: Tags that need both an opening and closing tags. Eg:- <HTML>...</HTML>
Empty tags: Tags with no closing tag Eg:-<BR> or <IMG>.
A tag pair plus everything between them is called an element. HTML itself is not case-sensitive.

Any plain text editor (Geany, Notepad, Notepad++) can write HTML — the file just needs to be saved with a .html or .htm extension, then opened in a browser to view it.

The four tags every page needs: <HTML> (wraps the whole document; Dir for text direction, Lang for language), <HEAD> (metadata section), <TITLE> (browser tab text), and <BODY> (the visible content — with attributes like Bgcolor, Background, Text, Link/Alink/Vlink for hyperlink colours, and Leftmargin/Topmargin).

Headings <H1>–<H6> scale from biggest to smallest. <P> makes paragraphs (collapsing extra spaces/lines automatically); <BR> forces a single line break without starting a new paragraph; <HR> draws a horizontal rule. Text styling tags include <B>, <I>, <U>, <S>/<STRIKE>, <BIG>, <SMALL>, <STRONG>, <EM>, and <SUB>/<SUP> for subscripts and superscripts. <BLOCKQUOTE> indents a long quotation, <Q> handles a short inline one. <PRE> preserves whitespace and line breaks exactly as typed; <MARQUEE> scrolls content; <DIV> groups a block for styling; <FONT> sets size/colour/face for a text span; <CENTER> centres its content.

Characters like < and > are part of HTML's own syntax, so typing them literally would confuse the browser. HTML entities (e.g. < for <, > for >) let these reserved characters appear as visible text instead.

Comments (<!-- like this -->) document the code for other readers without affecting what the browser displays — good practice in any document beyond the simplest.

<IMG> is an empty tag whose main attribute, Src, points to the image file. Other attributes control Height/Width, Border thickness, Align (how text wraps around it), and Alt — fallback text shown if the image fails to load, and read aloud by screen readers.