Hi,
by default, the left sidebar is determined only for a menu. To put there some widgets, you will need to create a child theme, register a new widget area and output it in “header.php”, right after this code:
<div class="menu-box">
<?php wp_nav_menu( array( 'menu_id'=>'nav', 'theme_location'=>'main-navigation' ) ); ?>
</div>
Best regards,
Tomas Toman