1. What is PHP?

PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used, open-source server-side scripting language designed specifically for web development. Unlike client-side languages such as JavaScript or HTML that run inside the user's web browser, PHP executes directly on the web server.

2. Client-Side vs Server-Side Architecture

Understanding the distinction between client and server execution is fundamental:

• Client-Side (Browser): Receives HTML, CSS, and client-side JavaScript. The browser renders visual layouts, handles animations, and triggers client events. The user can view the page source code.
• Server-Side (PHP): When a client requests a .php file, the web server executes the PHP engine, queries databases, processes logic, and returns pure, compiled HTML back to the browser. The raw PHP code is never exposed to the client.

3. How Web Servers Process PHP

A typical PHP request follows this request-response cycle:

1. User types a URL (e.g., https://example.com/profile.php) into their browser.
2. The Web Server (such as Apache or Nginx) receives the HTTP request.
3. The server recognizes the .php extension and routes the script to the PHP Interpreter (often via PHP-FPM or mod_php).
4. PHP executes business logic, fetches necessary records from a database (like MySQL or PostgreSQL), and generates dynamic HTML.
5. The resulting HTML is returned to the client browser over HTTP/HTTPS.

4. Setting Up a Local Development Environment

To run PHP on your local computer, you need a web server, PHP interpreter, and a database management system. Popular pre-configured software stacks include:

• XAMPP (Cross-Platform, Apache, MariaDB/MySQL, PHP, Perl) – available for Windows, macOS, and Linux.
• WampServer / Laragon – highly optimized for Windows web developers.
• MAMP – standard stack for macOS and Windows.
• Docker – modern containerized workflow for production parity.

5. Your First PHP Script

PHP code is enclosed within special starting and closing processing tags: . You can seamlessly interleave PHP within standard HTML documents.

    
    


    

    
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6. Summary & Best Practices

• Always save files containing PHP code with the .php extension.
• Never rely on client-side validation alone; server-side execution with PHP is required for authentication, payments, and data integrity.
• Ensure your web server has proper directory permissions and keep your PHP version updated (PHP 8.1+ recommended).