I need the feature where you have the menu, them a dropdown with different options, and when you hove into one of those dropdown menus it shows up images of every post related to that category

Example: in this page http://soledad.pencidesign.com/soledad-food/ when you hover into recipes, shows up different categories like breakfast, desserts and vegetarians, and them if you hove in one of those categories it shows up images which represent that specific post

how can achieve that?