Topic: How to get small description below menu item

hello guys,
m new to joomla and just want to learn that how can we get a small description of a menu item  when we hover mouse over that menu item.
for example i have uploaded one file. in this when we hover our mouse over "GOOGLE" a small box appears written '"google".
so i want to apply this functionality over menu items.

does anybody have any suggestions regarding this???

Thanks