How do I display the next 3 posts in the sidebar?

$args  = array( 'numberposts' => 3, 'offset' => 5 );
$posts = get_posts( $args );

foreach( $posts as $post ){

  setup_postdata( $post );

  [output the post here with the_title(), the_content(), etc]

}

If you search in the codex with ‘query posts’, you will find a lot.