You’re _doing_it_wrong(). When you call wp_nav_menu(), you should be referencing theme_location, not menu.
The way the custom navigation menu functionality is intended to work:
- The Theme registers locations for navigation menus to appear, via
register_nav_menus( array( 'location_slug' => 'Location Name' ). - Then the Theme instructs WordPress where to output those menus, via
wp_nav_menu( array( 'theme_location' => 'location_slug' ) ). - The user defines the menu itself, via the UI at
Dashboard -> Appearance -> Menus - Then the user assigns a defined menu to the Theme-registered locations, via that same UI.
So, by calling menu instead of theme_location in your wp_nav_menu() call, you prevent the user from assigning a menu to that location. Very likely what’s happening is that the user hasn’t defined a menu with the name you’re calling via the menu argument, and so WordPress is simply falling back to the default wp_page_menu() output.
Once you correct this issue, then you can define a menu with whatever links in it that you want, and then assign that menu to the appropriate location.