You need to check WordPress template-hierarchy how it works.
Single Post #
The single post template file is used to render a single post. WordPress uses the following path:
1.single-{post-type}.php – First, WordPress looks for a template for the specific post type. For example, post type is product, WordPress would look for single-product.php.
2.single.php – WordPress then falls back to single.php.
3.index.php – Finally, as mentioned above, WordPress ultimately falls back to index.php.
Page #
The template file used to render a static page (page post-type). Note that unlike other post-types, page is special to WordPress and uses the following patch:
1. custom template file – The page template assigned to the page. See get_page_templates().
2. page-{slug}.php – If the page slug is recent-news, WordPress will look to use page-recent-news.php.
3.page-{id}.php – If the page ID is 6, WordPress will look to use page-6.php.
4. page.php
5. index.php
For specific id you can use page-{id}.php
template.