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I would a bit more detail (or your starting code ) to see where you’re putting this or how you want to use it but from what I see you need to add a counter to your iteration and then use a modulo operator:

a sample query would look like this though:

$winnners_query = new WP_Query(array(
  'post_type' => 'post',
  'posts_per_page' => '10',
));

if ($winnners_query->have_posts()) {
  $i=1;
  $section=1; //section counter
  $count = $winnners_query->found_posts;  //total post count
  echo '<section class="side" data-role="side" id="section-section'.$section.'">'; //adds first section (you need to add css to style)
  while ($winnners_query->have_posts()) {
    $winnners_query->the_post();
    echo '<div class="content">'.get_the_title().'</div>'; //adds content you need to add css styles
    if ( $count == $i) {
        //we're on the last post of the query.  Close section
        echo '</section>';
    } else {
      if ($i % 2) { //if iteration is even increase section count, close section and open a new one
        $section++;
        echo '</section><section class="side" data-role="side" id="section-section'.$section.'">';
      }
      $i++;
    } 
  }
  wp_reset_postdata();
}