Q:

$wpdb error cant fix

i create custom plugin and i have table wp_customers , i try to select all things in my table but wordpress just show me Fatal error: Uncaught Error: Call to a member function get_results() on null in C:\xampp\htdocs\wordpress\wordpress\wp-content\plugins\rflredirection\public\showResult.php:4 Stack trace: #0 {main} thrown in C:\xampp\htdocs\wordpress\wordpress\wp-content\plugins\rflredirection\public\showResult.php on line 4
i see codex , i use some antoher codes for select but i just that massege , this is my codes to try
global $wpdb;

$results = $wpdb->get_results('SELECT * FROM $wpd->wp_customers DESC ');

and 
$results = $wpdb->get_results('SELECT * FROM wp_customers');

and
$table_name = $wpdb->prefix . "wp_customers";
$results = $wpdb->get_results("SELECT code FROM ".$table_name");

and i try get version but nothing
$dbVersion = $wpdb->db_version();
if ($dbVersion) {
    echo "Running MySQL " . $dbVersion;
} else {
    echo "MySQL version unavailable.";
}

A:

When you use The wpdb Class, there is no need to include wp_ in tables name.
should be just like this:
global $wpdb;
$results = $wpdb->get_results("SELECT * FROM $wpdb->customers");
//                                                  ^ use without (wp_)

Edit #1:
you have an error on foreach loop:
you should write foreach($results as $rows) instead of your error : foreach($rows as $results)
and don't forget the semicolons when get values, echo $rows["id"]; and so on..
your code should like:
<?php
 global $wpdb;
 $results = $wpdb->get_results("SELECT * FROM $wpdb->customers");
?>
<body>
 <table> 
    <tr> 
        <th>‌ID</th>
         <th>Name</th> 
         <th>Family</th>
          <th>Numbers</th> 
          <th>Tell</th> 
      </tr>
       <?php foreach($results as $rows){
        ?> 
        <tr> 
            <td>
                <?php echo $rows["id"]; ?>
            </td> 
            <td>
                <?php echo $rows["name"]; ?>
            </td> 
            <td>
                <?php echo $rows["family"]; ?>
            </td> 
            <td>
                <?php echo $rows["numbers"]; ?>
            </td> 
            <td>
                <?php echo $rows["tell"]; ?>
            </td>
             <?php }?> 
         </tr>
</table>

Edit #2:
Copy all this lines and paste on top of your page to include wordpress package:
<?php
/**
 * WordPress User Page
 *
 * Handles authentication, registering, resetting passwords, forgot password,
 * and other user handling.
 *
 * @package WordPress
 */

// Make sure that the WordPress bootstrap has run before continuing.
require( dirname(__FILE__) . '/wp-load.php' );

// Now your page codes goes here ...

