Example of drupal_render usage

<?php

//DRUPAL RENDER USAGE
$form['add_wf_mapping'] = array(
 '#type' => 'button',
 '#id'=>'edit-add-wf-mapping',
 '#name'=>'edit-add-wf-mapping',
 '#attributes' => array('style'=>'margin:0px'),
 '#value' => t('Map Workflow')
);
$output .=drupal_render($form['add_wf_mapping']);

echo $output;

Output  the button

?>