Post thumbnails-where do they appear?

http://designora.com/tools/wordpress-tricks-oembed/

In the template you can use the function the_post_image() to place the image anywhere you choose. Here is how to call the new function and the parameters for WordPress thumbnail image sizes.

<?php the_post_image(); ?>

the_post_image(); // without parameter = Thumbnail
the_post_image(’thumbnail’); // Thumbnail
the_post_image(’medium’); // Medium resolution

To add support for post thumbnails (and get admin-UI), add the following to your functions.php:

add_theme_support( ‘post-thumbnails’ );

You can read a lot more that and some “size-tricks” in Marks post:

http://markjaquith.wordpress.com/2009/12/23/new-in-wordpress-2-9-post-thumbnail-images/