Register sidebar

function alpha_sidebar(){
  register_sidebar(
      array(
          'name'          => __( 'Single Post Sidebar', 'alpha' ),
          'id'            => 'sidebar-1',
          'description'   => __( 'Right Sidebar', 'alpha' ),
          'before_widget' => '<section id="%1$s" class="widget %2$s">',
          'after_widget'  => '</section>',
          'before_title'  => '<h2 class="widget-title">',
          'after_title'   => '</h2>',
      )
  );
}

add_action("widgets_init","alpha_sidebar");