The WordPress template hierarchy is your friend.
https://developer.wordpress.org/themes/basics/template-hierarchy/
This provides a very detailed flow for how WP determines which template to load.
If you are ever uncertain about which template is loading, this little function is handy. Paste in your theme’s functions.php and it will display the template used at the bottom of the page.
add_action('wp_footer', 'wpse_show_template');
function wpse_show_template() {
global $template;
print_r($template);
}