function widgets_init_mysite() {
    register_sidebar( array(
        'name' => __( 'Main Sidebar', 'mytheme' ),
        'id' => 'sidebar-1',
        'before_widget' => '<div>',
        'after_widget' => '</div>',
        'before_title' => '<h3 class="widget-title">',
        'after_title' => '</h3>',
    ) );
}

add_action( 'widgets_init', 'widgets_init_mysite' );

$args = array(
    'name'          => __( 'Main Sidebar', 'mytheme' ),
    'id'            => 'sidebar-1',
    'before_widget' => '<div id="%1$s" class="widget %2$s">',
    'after_widget'  => '</div>',
    'before_title'  => '<h3 class="widget-title">',
    'after_title'   => '</h3>'
);
register_sidebar( $args );

<?php
// Dynamic Sidebar
if ( !function_exists('dynamic_sidebar') || !dynamic_sidebar('sidebar-1') ) :
    // Sidebar fallback content
    get_sidebar();
endif;
// End Dynamic Sidebar Single posts
?>