create_cat.php

<?php
//create_cat.php
include 'connect.php';
include 'header.php';

if($_SERVER['REQUEST_METHOD'] != 'POST')
{
    //the form hasn't been posted yet, display it
    echo "<form method='post' action=''>
        Category name: <input type='text' name='cat_name' />
        Category description: <textarea name='cat_description' /></textarea>
        <input type='submit' value='Add category' />
     </form>";
}
else
{
    //the form has been posted, so save it
    $sql = "INSERT INTO categories (cat_name, cat_description) VALUES ('mysqli_real_escape_string($connected, $_POST['cat_name'])', 'mysqli_real_escape_string($connected, $_POST['cat_description'])')";
    $statement = $connected->prepare($sql);
    $statement->execute();
    $result = mysqli_query($connected, $sql);
    if(!$result)
    {
        //something went wrong, display the error
        echo 'Error' . mysqli_error($connected);
    }
    else
    {
        echo 'New category successfully added.';
    }
}
?>