User blog comment:DaNASCAT/Technical Update: February 26, 2013/@comment-4129195-20130226195951/@comment-1091639-20130226203426

Once you enable it on your wiki, every category page will have an option to toggle between 'Category List' and 'Category Exhibition' in the form of two little icons in the top-right corner of the page. The default option is 'Category List' which is why you might not have noticed any difference.

See this category for an example and this help page for more details.