/**
 * Implementation of hook_settings().
 */
function register_settings() {
  $form['register_foo_setting'] = array(
    '#type' => 'checkbox',
    '#title' => t('Enable foo?'),
    '#default_value' => variable_get('regiter_foo_setting', 0),
    '#description' => t('Should foo be enabled?'),
  );

  return $form;
}