Microdata makes it possible to search engines to understand important details about your site's content. Microdata provides Google and Bing with extra information about your content such as names, descriptions, dates and ratings. And, because search engines can understand your data more clearly, they often reward you with a higher ranking.
In Joomla, microdata support was quietly added in Joomla 3.3 which was released in April 2014. The best to way to provide microdata is by using your template.
Some templates provide microdata support, but many do not. If your template was released before April 2014, it probably doesn't support microdata and will need to be updated.
I'm going to show you how to test your template and then add microdata if needed.