How can PHP beginners effectively pass variables from an HTML form to a PHP script for processing?

To pass variables from an HTML form to a PHP script for processing, you can use the POST method in the form tag and access the variables using the $_POST superglobal array in the PHP script. Make sure to set the form's method attribute to "post" and include input fields with name attributes corresponding to the variables you want to pass.

<form method="post" action="process.php">
  <input type="text" name="username">
  <input type="password" name="password">
  <button type="submit">Submit</button>
</form>
```

In the PHP script (process.php), you can access the variables like this:

```php
$username = $_POST['username'];
$password = $_POST['password'];

// Process the variables as needed