Understanding the 'session_start()' Function in PHP

In PHP, the 'session_start()' function plays a critical role in maintaining session-specific data across multiple pages. According to the quiz question, the correct answer is that the 'session_start()' function is used to "Start a new PHP session". This statement is absolutely correct.

When you call the 'session_start()' function in PHP, it basically tells PHP to initiate a new session, or to resume an existing one. This function must be the first thing in your document before any HTML tags.

Sessions are a convenient way to store data for individual users against a unique session ID. This can be used to persist state information between page requests. Session IDs are normally sent to the browser via session cookies and the ID is used to retrieve existing session data.

Practical Application

For instance, consider an online shopping website. Each user while shopping can add various items to their cart. The information of these items and their quantities are stored in a unique session that is specific to each user. These sessions are initiated using the 'session_start()' function in PHP.

<?php
// Starting session
session_start();

// Storing session data
$_SESSION["item1"] = "Book";
$_SESSION["item2"] = "Pen";
?>

In another or subsequent script, you might use something like the following to print out the session information:

<?php
// Starting session
session_start();

// Accessing session data
echo 'The items in the cart are: ' . $_SESSION["item1"] . " and " . $_SESSION["item2"];
?>

Just be aware, session_start() must be called before any output is sent to the browser, or else you may get an error about headers already being sent.

In conclusion, 'session_start()' is a powerful function in PHP that facilitates the process of storing and maintaining data across different pages of a web application. It proves to be quite a useful tool especially while creating websites that demand data persistence such as user logins, shopping carts, game scores, and more. Using it effectively is a testament to strong PHP development practices.