Bitrix Dialog box example more on that here: http://alexvaleev.ru/popup-window-bitrix/

bx_dialog_box.php

<? 
CUtil::InitJSCore( array( 'window' ) ); // load Bitrix's window library 
$APPLICATION->AddHeadScript( '/js/jquery.min.js' ); // load jQuery
?>

<? ob_start(); // start capturing HTML output ?>
<p>Some HTML content...</p>
<?
$content = ob_get_contents(); // save output info variable
$content = str_replace( array( "\n", "\r" ), '', $content ); // remove EOL-s - content: attribute of the BX.CDialog() requires that!
ob_end_clean(); // clean buffer
?>

<a class="show-window" href="">Open window</a>

<script type="text/javascript">
  jQuery(document).ready(function ($) {

    var Dialog = new BX.CDialog({
      title: "Window Title",
      head: "Content before main content",
      content: '<?= $content ?>',
      icon: 'head-block',
      resizable: false,
      draggable: true,
      height: 400,
      width: 600,
      buttons: [BX.CDialog.btnCancel]
    });

    $('.show-window').click(function (__event) {
      Dialog.Show();
      __event.preventDefault();
    });

  });
</script>