Fold Page List would typically be used to replace the functionality provided by the wp_list_pages tag that is usually found in the sidebar.php file in your active theme, itself located in wp-content/themes folder of your installation. To use, simply replace the code fragment that looks like this
<?php wp_list_pages ($arglist); ?>
with this:
<?php wswwpx_fold_page_list ($arglist); ?>
You can even use the same arguments as in the original call.
$arglist is optional and conforms exactly to those supported by the wp_list_pages tag that comes with WordPress 1.5, and which is explained in the Wordpress Codex.