Here is the method I use to call one of my manually created menus in WordPress as my main navigation menu.
First, you obviously need to create the menu and add the links you want to it. You can do this by logging into the dashboard and going to Menus under Appearance in the sidebar.
Once you have the menu created, go to Editor under Appearance in the sidebar.
Open the header.php template file.
Find the line of code that calls the default pages menu. It should look something like this:
<?php wp_nav_menu( array( 'container_class' => 'menu-header', 'theme_location' => 'primary' ) ); ?>
And replace it with this:
<?php wp_nav_menu( array( 'container_class' => 'menu-header', 'menu' => 'main' )); ?>
Make sure you replace the word “main” in the code above with the name of the menu that you want to use for your main navigation menu.