In the function widget( $args, $instance )
, which generates the widget output, add the following code before the echo $after_widget;
line:
// The Query
$the_query = new WP_Query( array( 'post_type' => 'page', 'posts_per_page' => '3' ) );
// The Loop
while ( $the_query->have_posts() ) :
$the_query->the_post();
echo '<li>' . get_the_title() . '</li>';
endwhile;
Additional information can be found on the WordPress Codex.