Showpost and last

Try this :

$the_query = new WP_Query( array(
            'post_type' => 'ad',
            'posts_per_page' => 10,
            'orderby' => 'date',
            'order' => 'DESC',
            'tax_query' => array(
                                array(
                                'taxonomy' => 'ad_category',
                                'field' => 'id',
                                'terms' => array('8')
                                )
                            )
    ));

• posts_per_page tells how many items you want to retrieve from DB
• orderby tells to order items by date (optional as this is the default value)
• order is set to DESC to retrieve from newest to oldest items