PHP Introduction

PHP stands for Hypertext Preprocessor. It is a widely-used, open-source scripting language designed specifically for web development. PHP code runs on a web server — not inside a browser — and it generates HTML output that the browser receives and displays.

PHP powers a significant portion of the internet. WordPress, Facebook (in its early years), Wikipedia's MediaWiki, and many e-commerce platforms are all built using PHP. Learning PHP opens the door to building dynamic, data-driven websites and web applications.

What Makes PHP Different from HTML

HTML is a static language. Once a web page is written in HTML, its content stays the same every time someone loads it. PHP is dynamic. A PHP script can change what it displays based on user input, data from a database, the current time, or any other condition.

Think of HTML as a printed flyer and PHP as a salesperson who reads the customer's name and prints a personalized letter every single time someone asks for one.

How PHP Works

When a visitor requests a PHP page, the following steps happen behind the scenes:

The browser sends a request to the web server for a .php file.
The server passes the file to the PHP interpreter.
PHP runs the code inside the file — querying databases, processing logic, and generating output.
The result (usually plain HTML) is sent back to the browser.
The browser displays the output. The visitor never sees PHP code — only the result.

Where PHP Runs

PHP requires a server environment to execute. The three most common setups are:

XAMPP — A free local server package for Windows, Mac, and Linux that includes Apache, MySQL, and PHP.
WAMP / MAMP — Similar local server packages specific to Windows and Mac respectively.
Online hosting — Most web hosting providers support PHP by default.

For practice, installing XAMPP on a local machine is the simplest starting point. Once installed, PHP files are placed in the htdocs folder and accessed through http://localhost/ in a browser.

PHP File Structure

A PHP file has the .php extension. It can contain plain HTML, PHP code, or a mix of both. PHP code is always written inside opening and closing PHP tags.

Basic PHP File Example

<!DOCTYPE html>
<html>
<body>

<?php
  echo "Hello, World!";
?>

</body>
</html>

In the example above, <?php marks where PHP code begins and ?> marks where it ends. The echo statement outputs the text Hello, World! to the browser.

What PHP Can Do

Generate dynamic page content based on user input or database data.
Create, open, read, write, and delete files on the server.
Collect and process form data submitted by users.
Send and receive cookies to track user sessions.
Add, modify, and retrieve data from databases like MySQL.
Control user access and manage authentication.
Encrypt sensitive data.

PHP Versions

PHP has evolved significantly over the years. PHP 5 introduced object-oriented programming features. PHP 7 brought major performance improvements. PHP 8 added named arguments, union types, match expressions, and the JIT compiler. The examples in this course are compatible with PHP 7.4 and above.

Key Points

PHP is a server-side scripting language used to build dynamic web pages.
PHP code runs on the server, not in the browser.
PHP files use the .php extension.
PHP code is placed between <?php and ?> tags.
A local server like XAMPP is needed to run PHP on a personal computer.
PHP can interact with databases, handle files, process forms, and manage sessions.

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