How to call form function in menu callback in drupal7?
After some sort of study, I got to the answer. we can get form by using drupal_get_form and then in return function, we need to render it also.
for example:

function component_list_edit() {
  $form = drupal_get_form('component_type_select_list_form');  
  // Load the modal library and add the modal javascript.
  ctools_include('modal');
  ctools_modal_add_js();
  return '&lt;div class="title_display"&gt;Title:'._mid_component_make_link('Title').drupal_render($form).'&lt;/div&gt;';
}