If you just want to echo a message from PHP in a certain place on the page when the user clicks the button, you could do something like this:
However, assuming your script needs to do some server-side processing such as adding the item to a cart, you may like to check out jQuery's http://api.jquery.com/load/ - use jQuery to load the path to the php script which does the processing. In your example you could do:
This runs the php script and loads whatever message it returns into order_item.php would add the item to cart and just echo whatever message you would like displayed. To get the example working this will suffice as order_item.php: For this to work you will need to include jQuery on your page, by adding this in your
tag: