Go to the Admin panel, themes & layouts, then go to "edit main menu"
Here is a picture showing you how to do a drop down menu.http://gyazo.com/9cdc6da7 ... 8a4543c139c16a1a906f
Make sure it is under the main page you want to drop down. It doesn't have to drop down on the first link. You can move it down to the last link you have. All personal choice. Hope this helped, if it didn't you can email me/ message me on the forums and I will be happy to go into more detail.