Hello Igor,

the right sidebar is not widgetized its role is more of a panel than a sidebar.

if for example you want text in the right sidebar of a Portfolio page (http://clapat.ro/themes/square-wordpress/) look for 

<!-- Sidebar -->
<div id="sidebar" class="hidden"></div>
<!--/Sidebar -->

in portfolio-page.php and add the text inside the div

Igor,

the left and right sidebars are not widgetized - they are more like panels, or frames

- left sidebar (the one that opens) : you can add any html code to Appearance -> theme options -> header options -> Menu Slogan Content

if you want to achieve more than that in /sections/menu_section.php

<?php
$squares_menu_slogan_title = squares_get_theme_options( 'clapat_sqr_menu_slogan_title' );
if( !empty( $squares_menu_slogan_title ) ){ 
?>
<p class="header-title"><?php echo wp_kses_post( $squares_menu_slogan_title ); ?></p>
<?php } ?>
<?php
$squares_menu_slogan_content = squares_get_theme_options( 'clapat_sqr_menu_slogan_content' );
if( !empty( $squares_menu_slogan_content ) ){ 
?>
<p><?php echo wp_kses_post( $squares_menu_slogan_content ); ?></p>
<?php } ?>

Your text here
<?php
get_template_part('sections/menu_social_links_section');
?>

- right sidebar in the Showcase Page open /sections/showcase_navigation_section.php and add your text here

<div id="open-sidebar"><img src="<?php echo esc_url( get_template_directory_uri() ); ?>/images/plus.png" alt="open">Your text</div>

I attach also latest version of WPBakery composer in case you need it

Hello Igor,

Add your text inside of a div:

<div class="vertical-text">Your text here</div>

in the <div id="open-sidebar"> after the plus image

Add the following CSS in customizer -> additional CSS:

.vertical-text {

    text-orientation: mixed;
    writing-mode: vertical-lr;
}