register_sidebar( array(
    'name'          => __( 'Header sidebar', 'langdomain' ),
    'id'            => 'headersidebar',
    'description'   => 'Sidebar in header',
    'before_widget' => '<div class="widget %2$s header-sidebar">',
    'after_widget'  => '</div>',
    'before_title'  => '<div class="widget-title">',
    'after_title'   => '</div>',

) );

<?php dynamic_sidebar( 'headersidebar' );