How do you start a session in PHP?

In PHP, sessions are a way to store data across multiple pages for a single user. This capability is crucial for maintaining state in web applications, as HTTP is a stateless protocol. To initiate a session in PHP, the session_start() function is used.

When session_start() is called, it checks if a session already exists by looking for a session identifier in the request. If a session does not exist, it creates a new session and generates a unique session ID. The session data can then be accessed via the superglobal $_SESSION array, which allows you to store and retrieve user-specific information across different pages.

This function must be called before any output is sent to the browser to ensure that the session headers can be properly sent. Understanding this function is fundamental for managing user sessions in PHP applications and is a key aspect of creating dynamic and interactive web experiences.