how to use custom page template in a page?

Your template should include the_content so that content from your editor is displayed in your page.

<?php the_content(); ?>

It would be better if you posted the php code of the page template you created, to find the exact issue.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)