Few days ago someone asked me how can he displays a custom message for a certain post, i went digging into the codex and found the following as a quick solution to embed in your code as it fit your theme needs.
open “single.php” in a text editor and added this line
<?php get_post_meta($post->ID, 'my-text', true); ?>
in the area you want the text to appear, usually its more useful if you have like a recipe website or something that needs certain data to be filled.
save your file.
then in the admin area –> post edit page; added custom field of name “my-text” and in the value field you can add your text.
hope it helps.