How can I create a new page template for the user registration page? I am a beginner in Drupal. I need to create a new page template for the registration page. Because in my website almost all pages have different layout.

Currently all pages are rendering through page.tpl.php.

Any suggestions?
There are so many ways to theming your registration page.
You can create user-register.tpl.php

To know about how to create user-register.tpl.php refer below links.

https://www.drupal.org/node/1211520

https://api.drupal.org/api/drupal/modules!user!user-profile.tpl.php/7

https://www.drupal.org/node/1195754

If you want to know how to create tpl files.

Page template suggestions are not working