On-topic answer:
You can just put <?php wp_login_form(); ?>
into any of your theme templates to render a login form on the front end of your site.
Or make your own shortcode [loginform]
by putting this into your theme’s functions.php
:
function wpse_242473_login_form() {
return wp_login_form( 'echo' => false );
}
add_shortcode( 'loginform', 'wpse_242473_login_form' );