hover over drop down menu

Hello everyone,

The site I’m working on is https://www.photocs.net. For the three main navigation categories (Travel, Portrait, Clients) I’d like to have a drop down menu appear when the user hovers/clicks on each of the categories. In the drop down list, I’d like to populate the sub-pages that belong to each category. Would this be easy to do? Could someone point me to some code please?

Thank you very much in advance!