[jQuery] Event trigger ajax event

[jQuery] Event trigger ajax event


I am confused when it comes to triggering an ajax event. I would like
to trigger a ajaxStart event, so I use:
$.event.trigger("ajaxStart");
But now, what will that trigger? What piece of code? Do I need to
have an $.ajax() function somewhere, so that when I trigger the
ajaxStart, it will pick up that ajax function?
Help me understand how these can work together!
Thanks!