How can we use form directly without using drupal form handler
If your goal is to just get the HTML output of an existing drupal form then this will get you there:

$form = drupal_get_form('drupal_form_id');
$form['#action'] = url('mypath');
print render($form); 


Replace 'drupal_form_id' with whatever registered Drupal form you want and url('mypath') with whatever URL you want to post to.