drop down menu for sub pages

I’m in the process of switching my site over to WordPress from RapidWeaver and need my Directory page to have a dropdown menu for the subpages in the directory. The current site is here: https://www.localsustainability.net and you can see how I have the menu for the Directory. I’m using the “grassy” theme in WP and would like to be able to have the directory menu do the same thing. I began trying Webdezine’s menu plugin, but it was putting a code error message in the body of each page (I don’t have that error message with me at the moment), and not creating any drop down for the subpages. Any suggestions or directions would be great.
Jim