A drop-down menu is a menu that you access by pressing down on a downward-pointing arrow.
 This arrow is usually found at the end of an item box with a default choice already in it.
  When you hold down on the arrow with your mouse, it opens a selection of choices. 
  While continuing to hold the left-mouse button pressed, slide down to your selection, then release. 
  Your selection will then become the item in the item box.