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");
});