Secondary navigation sample

secondary_nav_craftcms.twig

{# 
 # SECTION_NAME is name of section to generate secondary navigation for
 # parent, childernPages, child can be any name you choose.
 #}
 
{% set parent = craft.entries.section('SECTION_NAME').slug(craft.request.getSegment(1)).first %}
{% set childrenPages = parent.getDescendants(1) %}
 
<ul>
{% for child in childrenPages %}
    <li>{{ child.getLink() }}</li>
{% endfor %}
</ul>