add_shortcode( 'qg_shortcode', 'qg_shortcode' );
function qg_shortcode() {
$buffer = '<h3>Post Titles</h3>';
$q = new WP_Query(array(
'post_type' => 'post',
'posts_per_page' => 5
));
while ($q->have_posts()) {
$q->the_post();
$buffer = $buffer.get_the_title().'<br>';
}
wp_reset_postdata();
return $buffer;
}