Theming the login form in Drupal 7

Hello Ivan (sorry if I got your name wrong), I want to ask you.

Where can I read about how to customize the login form in Drupal?

I read this article

http://webtrue.org/content/temizaciya-drupal-7-forma-vhoda

and it didn't help me much, actually it didn't help at all. The login form disappeared and I don't know how to bring it back.

I hope there is similar material on your blog, thank you.