With PHP you can include a page inside your code inside a specific division.

for example inside index.php:

<div>

  <?php include('page2.php'); ?>

</div>

and inside page2.php you have:

<span>Hello World</span>

The result would be:

<div>

  <span>Hello World</span>

</div>

If what you want to achieve needs to be in the front-end as the user navigates through your site; that is after a click is made to an element and you don't want to change to another page, then AJAX is your option. this example is with Jquery:

$('.clickme').click(function(){

  $.ajax({

    url:'page2.php'

    success:function(msg){

      $('#insert_div').html(msg)

    }

  });

});

HTML:

<span class=clickme>Get Page 2</span>



<div id=insert_div>

  <!-- Page 2 will be inserted here -->

</div>

Another solution is Jquery load() as many have posted:

$('.clickme').click(function(){

  $('#insert_div').load(page2.php);

});