There is wordpress function get_post_meta, used to get custom field value of post.

<?php $meta_values = get_post_meta( $post_id, $key, $single ); ?>

$post_id is POST ID which you can get in loop. If you are not using default loop of wordpress then use global $post and then you can find post id value through $post->ID.
$key is for custom field name which you were insert from admin or code.
$single is optional. If set to true then the function will return a single result, as a string. If false, or not set, then the function returns an array of the custom fields.

Example:
Key is featured_image then

 get_post_meta( $post_id, ‘featured_image’ );