The easiest way is to just use one of the many themes that supports drop-down hover menus.
But if you want to code it yourself:
The wp_list_pages function automatically lists child pages as nested unordered lists like this:
<ul>
<li>Parent Page 1</li>
<li>Parent Page 2
<ul>
<li>Child Page 1</li>
<li>Child Page 2</li>
</ul>
</li>
<li>Parent Page 3</li>
</ul>
(Note that the Parent Page 2 li tag doesn’t close until after the nested list is closed.)
So from that you have to make your elements look something like this in style.css:
/* get rid of ugly pre-formatting */
ul {
list-style:none;
margin:0;
padding:0;
}
/* make the main navigation list horizontal */
ul li {
float:left;
padding:5px;
}
/* make the child navigation list vertical */
ul li ul li {
clear:both;
}
/* make the child list hidden by default */
li ul {
display:none;
}
/* make the child list appear when you hover over the parent */
li:hover > ul {
display:block;
}
That’s the basic functionality to get you started.
