adding featured image to wordpress post code example

Example 1: show featured image in post wordpress

 'class1 class2' ))
} else { ?>
  

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');