how to get the post ID from wp_insert_post

I’ve just tested your code in a function hooked on wp_body_open and it works:

add_action( 'wp_body_open', 'function_test' );
function function_test() {
    $tittle="My new page";
    $newPage = array(
        'post_type'     => 'page',
        'post_title'    => $tittle,
        'post_status'   => 'publish'
    );
    $post_id = wp_insert_post( $newPage);
    print_r($post_id);
}

Where do you use this code ?