Using ajax with wordpress

Question

I'm trying to get my head around ajax requests in Wordpress and am finding it hard to understand. Basically I have a form that has a number of steps and you move through these requests using ajax, posting the data each time and hiding and showing the div for the different steps that generally have form fields. Currently have a form that is executed in a plugin with a shortcode. This makes a ajax request in the following way:

function callAjaxsubmit() {
  $("#form").serialize();
  $.ajax({
     type: "POST",
     url: "/confirm.php",
     data: $("#confirm").serialize(),
     success: function(data) {
         $( ".page-error-message" ).remove();
         $("#step3").html(data); 
         $("#step2").empty(data);
         $('html, body').animate({ scrollTop: 0 }, 'slow');
     }
  });
  return false;
}

I am trying to do this in the frontend, I have looked at this: http://codex.wordpress.org/AJAX_in_Plugins and many tutorials but just not sure how to apply that to this. I guess I need to call a function rather then a url?

Update: well, got it triggering the fucntion now, though having problems with the post data. I have a lot of fields and before I was doing toe ajax the proper wordpress way i was using serialize() to get all form data, but that doesn't seem to work properly, it seems to output it into one long string. is there a special way to serialize() the post data?

Update2: sorted the serialize issue with the following:

var formData =  'action=wordpress_function&' + jQuery("#form").serialize();
  jQuery.ajax({
    type: "POST",
    url: MyAjax.ajaxurl,
    data: formData,
        success: function(data) {  
            //do stuff
        }
  });
  return false;

Answer 1

In Wordpress Ajax works this way:

First, you register the ajax action and the function you want to use to serve that action, of course, you have to write that function.

All the request go to the same URL wp-admin/admin-ajax.php, what it changes is the action, and depending on the action, a different function is called.

The function you call, returns the result, which you get as the response in the ajax request.

If you have any doubts of any step just ask.