Categories Going to different Blog Pages?

One way would be to create a template page, and in that page, you’d have the logic to display the categories you want to show. Your template page would look something like this:

/*
Template Name: Secondary Blog Page
*/

get_header();

/*Code for your custom category display*/
$customcats = new WP_Query(array(
    'cat' => 12,13,15  //Category ID's
));
if($customcats->have_posts()):

while($customcats->have_posts()): $customcats->the_post();
    //code to display the posts however you want
endwhile;

endif;
wp_reset_postdata();

get_sidebar();
get_footer();

Then you’d create a new page, and choose this template to render it.