how to make a custom module that has three forms on one page I know how to make a module that has one form : http://www.wdtutorials.com/2012/04/26/drupal-7-how-create-forms#.U_YI1WNab3s

But how can I make a module that contains three different forms on the same page?
Yes you can create as many as forms in one page.
One method is using drupal render function.
Example:

$f = drupal_get_form('call_your_form');
$f1 = drupal_get_form('call_your_form1');
echo  drupal_render($f).drupal_render($f1);


Like this you can display any number of from in one page.