How to add the Terms and Conditions to custom form,not using any profile 2 or webform module?
You can just add another element to the form like so:

$form['terms'] = array(
  '#type' =&gt; 'checkbox',
  '#title' =&gt; t('Terms &amp; Conditions'),
  '#prefix' =&gt; "&lt;p&gt;Your terms go here&lt;/p&gt;",
  '#required' =&gt; TRUE,
);


That will just stick the text before the checkbox, and then use CSS to position it however you want.

You might also want to put a validate hook in there and remove the #required attribute so you can write your own text in the form_set_error.