I just want to show message in popup when user register to site."Further instructions have been sent to your e-mail address". This message i want to show in pop-up.
Use this module to show popup on the specific page.Use the latest dev version https://drupal.org/project/popup_message
You can check Better message module for this purpose.
From the module's project page:
Better Messages is a very simple module that provides "Popup-like" Drupal messages.
Better Messages intends to let you control where and how you want to see your Drupal messages! Combine different animations and override
better_messages.tpl.phpto create your custom look.