The purpose of Navigation Groups is to give you a way to create a small subset of site navigation – perhaps to show key links in the footer of your site. You should not need to place your main navigation into a Navigation Group – this is not what they were designed for and usually leads to problems!
The standard Navigation functions should be all you need to display main and sub-navigation. Use Navigation groups to allow your content editors to select and order small groups of links.
Creating a Navigation Group
You create groups in the Perch Admin under
Pages > Navigation Groups.
Once you have a group or groups these will appear in the Page Options for each page, to add a page to a group check the relevant checkbox.
The pages will then be listed under the Navigation Group where you can reorder them.
Displaying a group on your site
To display a navgroup on your site you use the standard Navigation Functions and include the navgroup slug. If I have created a navgroup for footer navigation called footer, I could add the following block to the page:
<?php perch_pages_navigation(array( 'navgroup' =>'footer', 'levels' => 1 )); ?>
This would add the pages in that navgroup, if the content editor added pages or re-ordered them this would now be reflected on the site.