index.html

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Google Ad Manager Set Targeting</title>
  <script async src="https://securepubads.g.doubleclick.net/tag/js/gpt.js"></script>
  <script>
    window.googletag = window.googletag || { cmd: [] };
    googletag.cmd.push(function () {
      //set ad uunit level targeting
      googletag.defineSlot('/19968336/test_Ad_unit', [[300, 250]], 'test_Ad_unit')
        .addService(googletag.pubads())
        .setTargeting("position", "btf");//targeting line, first argument is key and second is value
      googletag.pubads().enableSingleRequest();
      googletag.enableServices();
    });

    // set page level targeting
    // apliying to all ad units
    googletag.cmd.push(function () {
      googletag.pubads().setTargeting('page_type', 'article');//first argument is key and second is value
      googletag.pubads().setTargeting('page_path_name', window.location.pathname);//first argument is key and second is value
    });
  </script>
</head>

<body>
  <div id="test_Ad_unit">
  </div>
</body>

</html>