Codex for Admin Functionality

Hi,
I need to be able to update navigation menus through an external part of the system. I have included the wordpress load file, and used functions to create categories etc just fine.
What function would I need to call and what parameters would I need to pass to add new navigation items to custom menu for use with wp_nav_menu?
Also I’m sure that I will need to create other functionality to integrate in wordpress, is there any list of functions anywhere which will point me to their respective entries in the codex?

Regards
John