Drupal - Just want to add HTML to a node's form element how?
Create own helper module. Use hook_form_alter(), specifically hook_form_node_form_alter() variant. In it, just add #markup element.

$form['my_markup'] = array(
  '#markup' =&gt; "Your HTML here",
);


But in content of your question, it seems you want more than own html. It looks like you want to add some active elements. So see Form API Reference for elements you need. To process values, you will need to define submit handlers.