Question How to write into the database

1. Create file 1.php

PHP:

<?php
print'<form action="http://site.com/callback.php" method="post">
<input type="text" name="simple_text"  value="Test text into DB" />
<input type="submit" value="Submit" accesskey="s" class="button primary" />
</form>';
?>

http://site.com/1.php

2. Need field simple_text write into the database
Create file callback.php

http://site.com/callback.php

PHP:

<?php

$parentOfDirOfFile = dirname(dirname(__FILE__));
$scriptFilename = (isset($_SERVER['SCRIPT_FILENAME']) ? $_SERVER['SCRIPT_FILENAME'] : '');
$pathToCheck = '/ControllerPublic/SimpleText.php';
$fileDir = false;
if (file_exists($parentOfDirOfFile . $pathToCheck))
{
    $fileDir = $parentOfDirOfFile;
}
if ($fileDir === false AND !empty($scriptFilename))
{
    $parentOfDirOfScriptFilename = dirname(dirname($scriptFilename));
    if (file_exists($parentOfDirOfScriptFilename . $pathToCheck))
    {
        $fileDir = $parentOfDirOfScriptFilename;
    }
}
if ($fileDir === false)
{
    die('XenForo path could not be figured out...');

chdir($fileDir);

$simple_text = $_REQUEST['simple_text'];

require ($fileDir . $pathToCheck);


and all files http://xenforo.com/community/threads/how-to-read-and-write-into-the-database-with-a-page.23560/

How to write into the database field name="simple_text" value="Test text into DB"?