How do you add a widget to the side of a page

To register a sidebar widget, head over to Appearance > Editor and select the function.php from the right side. Then copy and paste this code at the end of your function.php file.

function custom_register_widgets() {
    register_sidebar( array (
        'name'          => __( 'Sidebar widget'),
        'id'            => 'sidebar-custom',
        'description'   => __( 'Widgets dragged here will appear in the right sidebar.' ),
        'before_widget' => '<aside id="%1$s" class="widget %2$s">',
        'after_widget'  => '</aside>',
        'before_title'  => '<h5 class="widget-title"><span>',
        'after_title'   => '</span></h5>'
    ) );    
}

add_action( 'widgets_init', 'custom_register_widgets' );

Now you need to call your widget in order to display it. Again from the right side, select sidebar.php and paste this code in the place you need:

<?php
if(is_active_sidebar('sidebar-custom')){
dynamic_sidebar('sidebar-custom');
}?>