a page with categories and posts

create a page template, possibly starting with a copy of page.php (depends on your theme);
https://codex.www.ads-software.com/Pages#Page_Templates

the main code could be (no html structure included):

<?php
$cat = get_term_by('name','AMERICA','category');
if( $cat) foreach( get_categories('parent='.$cat->term_id) as $sub_cat) {
echo $sub_cat->name; //OUTPUT SUB CATEGORY TITLE
$args = array(
'category__in' => array($sub_cat->term_id),
'posts_per_page' => -1
);
$sub = new WP_Query( $args );
if( $sub->have_posts() ) : while( $sub->have_posts() ) : $sub->the_post();
//YOUR POST OUTPUT CODE//
endwhile; endif; wp_reset_postdata();
}
?>

https://codex.www.ads-software.com/Function_Reference/get_term_by
https://codex.www.ads-software.com/Function_Reference/get_categories
https://codex.www.ads-software.com/Class_Reference/WP_Query

Hi,
Thanks for your answer.
It does not work for me.
I’m reading documentatiion.
If you have any idea, I even do not see the man category (according to my example America, countries to be sub cat and cities to be posts titles)