This page refers to the Control Panel's side-bar navigation. Not to be confused with "Navs", where you can create trees to be used for the front-end of your site.
Accessing CP Nav Preferences
Users can access CP Nav preferences through the cog icon in the upper right hand corner of the CP.
Customizing CP Nav Preferences For Other Users
In order to customize CP nav preferences for other users, you must first enable Statamic Pro, and you must either be a super user or have permissions to manage preferences.
This will allow you to customize the default CP nav for all users, or on a role-by-role basis, though end-users will still have the ability to further customize their own CP nav as they see fit.
Extending Via Addon
On top of allowing the end user to customize their CP nav, Statamic also provides PHP helpers for extending the CP navigation within an addon.