[jQuery] Event trigger ajax event

[Nic Hubbard]

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!