In WordPress the user can create their own menus in the CMS area by just going to Appearance -> Menus.
From this page you can then assign these menus to locations in the theme by choosing the theme location for the menu. These theme locations are setup by the theme developer and is done by using the function register_nav_menus();
The register nav menu function can be placed in the functions.php file.
To find out more about this continue reading here.
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