To get the menu to automatically drop on hover then this can achieved using basic CSS. You need to work out the selector to the hidden menu option and then set it to display as block when the appropriate li tag is hovered over. Taking the example from the twitter bootstrap page, the selector would be as follows:

ul.nav li.dropdown:hover > ul.dropdown-menu {
    display: block;    
}

However, if you are using Bootstrap’s responsive features, you will not want this functionality on a collapsed navbar (on smaller screens). To avoid this, wrap the code above in a media query:

@media (min-width: 992px) {
  ul.nav li.dropdown:hover > ul.dropdown-menu {
    display: block;
  }
}

Then to make the dropdown’s appear more smoothly, we can apply a fade in effect as follows:-

.dropdown .dropdown-menu{
    display: block; 
    opacity:0;
    -webkit-transition: all 200ms ease-in;
    -moz-transition: all 200ms ease-in;
    -ms-transition: all 200ms ease-in;
    -o-transition: all 200ms ease-in;
    transition: all 200ms ease-in;
}
.dropdown:hover .dropdown-menu {
    display: block;
    opacity: 1;
}

Hope this helps 🙂