how to get post id from function wordpres code example

Example 1: wordpress get post by id

$post   = get_post( 123 ); // Where 123 is the ID
$output =  apply_filters( 'the_content', $post->post_content );

Example 2: wordpress query a post by id

//WordPress: Query a specific post by its post type & ID
//For example, query Case Study with ID #12345

<?php query_posts('post_type=case_studies&p=12345'); ?>
  
/*To determine a post ID, refer to the
URL of the post while editing it:
http://localhost...wp-admin/post.php?post=12345...*/