First, creating your templates if you don't have them yet.
Page.php is the default page. Get that, replicate it and rename it; creating:
Now on top of those pages, you'll probably see this code
<?php get_header(); ?> add this code above that and on every page you created. *use different names for each.
Template Name: Template A
Upload the pages to your server/ within your theme files.
Now, go to edit your pages and under the "page attributes" > Templates > use the dropdown to select the template you created > update your page.