Requiring Once into plugin PHP File not working

I am trying to get a php file to input content into the wordpress database under a specific table. I have set up the table and have verified that the information is passed into the insert.php file. THe issue is that I can not include the global $wpdb and when i call for a required once on the wp_config file or the other required files it gives me this error in the php logs:

[22-Aug-2015 18:07:03 Europe/Berlin] PHP Fatal error: require_once(): Failed opening required 'http://explorejeff.city/site1/wp-config.php' (include_path='.;C:\xampp\php\PEAR') in C:\xampp\htdocs\site1\wp-content\plugins\fbg-manager\inc\insert.php on line 8

I imagine it has to do with the insert.php file not being localized, however I am not familiar with how to localize a php file to allow for required php files to be included.

Insert.php

?php
$url = 'http://'.$_SERVER['HTTP_HOST'];

global $wpdb;

 if(!isset($wpdb))
{
require_once($url.'/site1'.'/wp-config.php');
require_once($url.'/site1'.'/wp-load.php');
require_once($url.'/site1'.'/wp-includes/wp-db.php');
} 

$groupid= $_POST['groupid'];
$groupname = $_POST['groupname'];

error_log(print_r($url,true), 3, "my_errors.log");

$user_ID = get_current_user_id();
$settings = $wpdb-prefix . "fbg_manager_settings"; 

$wpdb-insert( 
    $settings, 
    array( 
        'userid' = $user_ID, 
        'groupid' = $groupid,
        'groupname' = $groupname,      
    ) );

?