How to Create forms with custom html codes

If by 'html codes' you mean you want to theme your form page, then you could it by hook_theme().

/**
 * Implements hook_theme().
 */
function yourtheme_theme($existing, $type, $theme, $path) {
  $base = array(
    'render element' => 'form',
    'path' => drupal_get_path('theme', 'yourtheme') . '/templates/forms',
  );

  return array(
    'form_id' => $base + array(
      'template' => 'template-name',
    ),
  );
}

And you may find template suggestions handy in these type of situation, to get it add the following in settings.php,
$conf['theme_debug'] = TRUE;

If you want to wrap around your custom divs or want to add custom classes or ids or any other custom attribute to your form elements you can use the #prefix, #suffix and/or #attributes
e.g.

$form['example_field'] = array(
  '#type' => 'text',
  '#title' => t('some title'),
  '#prefix' => '<div class="test">', //this will add your custom html tags as starting field wrapper
  '#suffix' => '</div>', //this will add your custom html tags as ending field wrapper
  '#attribute' => array(
  				'class' => array('class-one', 'class-two'),
  				'id' => 'test-id',
  				'placeholder' => 'this is field placeholder',
  			),
);

You can add more attrbitues to #attributes there is no limit on it.

you can use below code to use HTML in your form.

$html = '<div id="fiber3">
        <div class="row"><h4 class="col-sm-6">1 GB</h4><p class="col-sm-6 text-right"><small></small></p></div>
        <div class="progress">
          <div class="progress-bar progress-bar-success" role="progressbar"><span></span></div>
        </div>
      </div>';

$form['display_html'] = array(
        '#type'
            => 'markup',
            '#markup'
                => $html,
);