PHP Primer — Stack Picker

What is it?

PHP is a server-side programming language built specifically for the web. While JavaScript runs in the visitor's browser, PHP runs on the web server: when someone requests a page, the server executes your PHP code — reading a database, checking a login, processing a form — and sends back the resulting HTML.

It powers a huge share of the web (WordPress alone runs on PHP), and its killer feature for beginners is deployment: PHP comes pre-installed on virtually every shared hosting plan. Upload a .php file and it just runs — no server processes to manage, no configuration.

When to use it

PHP is the most practical choice when you're on shared hosting or building a traditional website — pages rendered on the server, a contact form, a small database-backed site. It pairs naturally with MySQL, which the same hosts also provide. If you're building a JavaScript-heavy single-page app or want one language across frontend and backend, Node.js may fit better.

Core concepts

Embedded in HTML — PHP code lives inside <?php ... ?> tags in otherwise normal HTML files. The server runs the code and the visitor only ever sees the output.
The request/response cycle — each page load is a fresh run of your script. Form data arrives in $_POST and $_GET; sessions ($_SESSION) carry data between requests.
Variables and arrays — variables start with $; PHP's array type doubles as both list and dictionary and is used everywhere.
Talking to databases — the built-in PDO library connects to MySQL and others. Always use prepared statements, which keep user input from being executed as SQL.
Escaping output — run user-provided text through htmlspecialchars() before printing it, so it can't inject scripts into your page.

A taste of the code

<?php
$name = $_GET["name"] ?? "world";
$hour = (int) date("H");
$greeting = $hour < 12 ? "Good morning" : "Hello";
?>
<!doctype html>
<html>
  <body>
    <h1><?= htmlspecialchars("$greeting, $name!") ?></h1>
  </body>
</html>

Save this as hello.php on any PHP host, visit hello.php?name=Sam, and the server builds the page for that visitor on the fly.

Your first steps

Install PHP locally (on Windows, XAMPP is the easy route; on Mac/Linux, PHP is a package install away), then run php -S localhost:8000 in your project folder for an instant dev server.
Make a page that uses date() and an if statement to greet visitors differently by time of day.
Build a contact form: an HTML form that posts to a PHP script which validates the input.
Connect to a MySQL database with PDO and build a tiny guestbook — insert and list messages. Learn some SQL alongside.
Upload your project to a shared host and see it run on the real web.

Go deeper

Official docs: php.net