Menu Help

Having a problem adding custom menus. The template I’m using doesn’t support menus. So I’m trying to overide that. From the “Navigation Menu” help page they instruct to add this:
To Function php

function register_my_menus() {
register_nav_menus(
array( ‘header-menu’ => __( ‘Header Menu’ ) )
);
}
add_action( ‘init’, ‘register_my_menus’ );

Then add this to the header php

<?php wp_nav_menu( array( ‘theme_location’ => ‘header-menu’ ) ); ?>

I get fatal errors. Can someone explain in more step by step detail?