I have multiple DIVs with unique IDs. Each DIV onclick slides down and shows some content below it.
I would like to track the clicks on each DIV to know which DIV is be
It sounds like you're looking for Google Analytics "Event Tracking." Assuming you already have your regular GA code snippet set up (to track your site), you can then set up a handler (for clicks of the div, let's say) do to something like this with jQuery:
$('.trackerClass').click(function() {
var selId = $(this).attr('id');
_gaq.push(['_trackEvent', 'Interactions', 'Click', selId]);
});
Every div that you wanted to track could have both "trackerClass" as the class, and a unique ID to help you identify it.
If you wanted to track opens/closes individually, you could add a state variable and pass that as well.
More information is available here:
https://developers.google.com/analytics/devguides/collection/gajs/eventTrackerGuide#SettingUpEventTracking
Edit: for straight JavaScript, kennis' answer will do it.