Never used that theme before, but it seems it doesn't have it built in by default.
You have to setup the template to display child pages.
This shows just the 1st level of children.
<ul id="nav">
<% loop Menu(1) %>
<% if Children %>
<li><a href="$Link" title="Go to the $Title.XML page">$MenuTitle</a>
<ul>
<% loop Children %>
<li><a href="$Link" title="Go to the $Title.XML page">$MenuTitle</a></li>
<% end_loop %>
</ul>
</li>
<% else %>
<li><a href="$Link" title="Go to the $Title.XML page">$MenuTitle</a></li>
<% end_if %>
<% end_loop %>
</ul>
You should then also use some type of script for browser compatibility like http://users.tpg.com.au/j_birch/plugins/superfish/