How to get multiple selected values of select box in php?

If you want PHP to treat $_GET['select2'] as an array of options just add square brackets to the name of the select element like this: <select name="select2[]" multiple …

Then you can acces the array in your PHP script

<?php
header("Content-Type: text/plain");

foreach ($_GET['select2'] as $selectedOption)
    echo $selectedOption."\n";

$_GET may be substituted by $_POST depending on the <form method="…" value.