For example you have an exported service endpoint like this:

$endpoint = new stdClass;
$endpoint->disabled = FALSE; /* Edit this to true to make a default endpoint disabled initially */
$endpoint->api_version = 3;
$endpoint->name = 'test';
$endpoint->server = 'rest_server';
$endpoint->path = 'test';
$endpoint->authentication = array();
$endpoint->server_settings = array();
$endpoint->resources = array(
  'node' => array(
    'operations' => array(
      'retrieve' => array(
        'enabled' => 1,
      ),
      'create' => array(
        'enabled' => 1,
      ),
      'update' => array(
        'enabled' => 1,
      ),
      'delete' => array(
        'enabled' => 1,
      ),
      'index' => array(
        'enabled' => 1,
      ),
    ),
    'relationships' => array(
      'files' => array(
        'enabled' => 1,
      ),
      'comments' => array(
        'enabled' => 1,
      ),
    ),
  ),
);
$endpoint->debug = 0;

and you want to put that exported service endpoint to a certain module (for example mymodule) so that when that module is installed in a different site, that exported service endpoint is already available on the Service page (in drupal 6 it is at admin/build/services/list).

To do that, in your mymodule.module, put the following hook:

/**
 * Implementation of hook_ctools_plugin_api().
 */
function mymodule_ctools_plugin_api($module, $api) {
  if ($module == 'services' && $api == 'services') {
    return array('version' => 3);
  }
}

And then, create a file named mymodule/mymodule.services.inc, inside that file, put your exported service endpoint:

function mymodule_default_services_endpoint() {
  $export = array();

  // begin exported service endpoint.

  $endpoint = new stdClass;
  $endpoint->disabled = FALSE; /* Edit this to true to make a default endpoint disabled initially */
  $endpoint->api_version = 3;
  $endpoint->name = 'test';
  $endpoint->server = 'rest_server';
  $endpoint->path = 'test';
  $endpoint->authentication = array();
  $endpoint->server_settings = array();
  $endpoint->resources = array(
    'node' => array(
      'operations' => array(
        'retrieve' => array(
          'enabled' => 1,
        ),
        'create' => array(
          'enabled' => 1,
        ),
        'update' => array(
          'enabled' => 1,
        ),
        'delete' => array(
          'enabled' => 1,
        ),
        'index' => array(
          'enabled' => 1,
        ),
      ),
      'relationships' => array(
        'files' => array(
          'enabled' => 1,
        ),
        'comments' => array(
          'enabled' => 1,
        ),
      ),
    ),
  );
  $endpoint->debug = 0;

  // end of exported service endpoint.

  $export['test'] = $endpoint;

  return $export;
}

Your service endpoint should be automatically listed in Service page once mymodule is installed.