hook_form()

  $form['overview'] = array(
    '#markup' => t('This interface allows administrators to manage general example Settings'),
    '#prefix' => '<p>',
    '#suffix' => '</p>',
  );

  $form['example_gmap'] = array(
    '#title' => t('Enable Google Maps'),
    '#description' => t('When enabled, Google Maps will be rendered if latitude and longitude are known.'),
    '#type' => 'checkbox',
    '#default_value' => variable_get('example_gmap', 1),
  );

  $form['default_center'] = array(
    '#title' => t('Map Center'),
    '#description' => t('Location of the center of the map of example.'),
    '#type' => 'fieldset',
    '#collapsible' => TRUE,
    '#collapsed' => FALSE,
  );

  $form['default_center']['example_default_center_lat'] = array(  //This is a nested array because we are talking about a fieldset
    '#title' => t('Latitude'),
    '#description' => t('Signed degrees format (DDD.dddd)'),
    '#type' => 'textfield',
    '#default_value' => variable_get('example_default_center_lat', 42.91455),
    '#required' => TRUE,
  );

  $form['default_center']['example_default_center_long'] = array(  //This is a nested array because we are talking about a fieldset
    '#title' => t('Longitude'),
    '#description' => t('Signed degrees format (DDD.dddd)'),
    '#type' => 'textfield',
    '#default_value' => variable_get('example_default_center_long', -75.569851),
    '#required' => TRUE,
  );

  $options = range(0, 20, 1);
  $options[0] = t('0 - Furthest');
  $options[20] = t('20 - Closest');

  $form['example_default_gmap_zoom'] = array(
    '#title' => t('Google Map zoom'),
    '#description' => t('Default level of zoom, between 0 and 20.'),
    '#type' => 'select',
    '#options' => $options,
    '#default_value' => variable_get('example_default_gmap_zoom', 8),
    '#required' => TRUE,
  );

  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Save'),
  );

  return $form;
}