Sessions in PHP (Login Memory Explained)

Sessions allow your website to remember a user across pages.

The mental model

• Browser sends request
• Server creates a session (a storage area)
• Browser stores only a session id (usually in a cookie)
• Each next request sends that id back
• Server uses it to find the user’s stored data

flowchart LR
  A[Browser] -->|Request| B[Server]
  B -->|Set session id cookie| A
  A -->|Next request with session id| B
  B -->|Load session data| C[Session Storage]

Step 1: Start session

Always call session_start() at the top before output:

<?php
session_start();
?>

Step 2: Store session values (like after login)

$_SESSION['user_id'] = 10;
$_SESSION['name'] = 'Jessica Miller';

Step 3: Read session values

if (isset($_SESSION['user_id'])) {
  echo "Welcome " . $_SESSION['name'];
}

Step 4: Logout

session_start();
session_unset();
session_destroy();

Next: Cookies in PHP and how they differ from sessions.