Can I use CiviCRM to track web use demographics on a joomla website?
Not really, maybe partially.

If you're looking to collect information from your users via a form, CiviCRM can help with that - but is probably overkill for your purposes.  If you want to know which pages your users are visiting, you're looking for an analytics tracking program, like Piwik or Google Analytics (or something fancier still).  People have occasionally linked CiviCRM with analytics tools, but that's a big-budget project.

Google Analytics will provide you with demographics and interest analysis in aggregate.  I'd start there and see how far that gets you before considering a tool like CiviCRM.