Question

The menu should pop up when mouse hover. As for comments on this site.

Answer 1

A quick example would look something like this:

HTML

<p>Hover me for more text...<span>see, I told you!</span></p>

CSS

p span { display:none; }
p:hover span { display:inline; }

Demo: jsfiddle.net/fWK2e

Expand on that concept and you can hide an element until it’s parent is hovered, revealing more content such as links or images, etc. Just know that the :hover pseudo-class doesn’t work on older browsers so you’ll have to resolve that with JS.