You need to use any of this module
Nice Menus enables drop-down/right/left expandable menus. It uses only CSS for most browsers, with minimal Javascript for IE6.
You will see several blocks called Superfish", move any of them to a region, use the "Configure" link of the block to configure it accordingly to your needs, and save.
Responsive Dropdown Menus provides a new menu tree rendering to make responsive, drop-down enabled main menu possible on any theme.
Provides new menu blocks for each menu. All module blocks add dropdown menu support and responsive menu toggles. Supports menu attributes
Mega menus are a type of drop-down, which seeks to overcome some of the usability drawbacks of traditional drop-downs. Hierarchy of your navigation is made visible all at once and the amount of clicking, searching, and navigating is reduced.