.

 In theme functions.php:

add_action( 'widgets_init', 'my_register_sidebars' );
function my_register_sidebars() {
	register_sidebar(
		array(
			'id' => 'primary',
			'name' => __( 'Primary' ),
			'before_widget' => '<div id="%1$s" class="widget %2$s">',
			'after_widget' => '</div>',
			'before_title' => '<h3 class="widget-title">',
			'after_title' => '</h3>'
		)
	);
}

In theme where you want widgets displayed:

<?php if(is_active_sidebar('primary')) : ?>
<div id="sidebar">
<ul>
<?php dynamic_sidebar('primary'); ?>
</ul>
</div>
<?php endif; ?>