how to display featured image in wordpress template code example

Example 1: wordpress featured image show

<?php echo the_post_thumbnail(); ?>

Example 2: add featured image

function fn_add_featured(){
   add_theme_support( 'post-thumbnails' );
   add_image_size( 'post-imge', 730, 380 );
}

add_action('after_setup_theme','fn_add_featured');