<?php
/*
* Plugin Name: WordPress ShortCode
* Description: Fules Plugin.
* Version: 1.0

*/

// Example 1 : WP Shortcode to display form on any page or post.
function form_creation(){

   global $wpdb;
?>
<form>

Liters:<select>
<?php
     $sql = 'SELECT liters FROM wp_tfp';
     $liters = $wpdb->get_col($sql);

if( $liters ) {
  foreach( $liters as $liter ) {
        echo '<option value="' . $liter . '">' . $liter . '</option>';
  }
}
?>
</select>
Price: <input type="text" name="price"><br>

</form>
<?php
}
add_shortcode('test', 'form_creation');
?>