custom fields show as metatags to insert into post ad:

<?php echo get_post_meta ($post ->ID, “field-name”, true?>
or (conditional)
<?php $field-name=get_post_meta ($post->ID,”field-name”,true);
if ($field-name){ ?>
<?php echo$field-name;?>
<?php } else {?>
<p>default message </p>
<?php }?>

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to display a custom field value outside of the loop:

<?php global $wp_query;
$post id=$wp_query ->post->ID;
echo get_post_meta($ post id, ‘custom-field-name’, true); ?>

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in loop:

<?php of(get_post_meta(post->ID,’thumbnail’,true));?>
<a href=”<K?php the permalink()?>”
rel=”bookmark” <img style=”float;left; margin:0px 10px 0px;” src=”<?php echo get_post_meta($post->ID,’thumbnail’,true);?> alt=”alt_text”?></a>

more info: http://wordpress.tv/2009/08/29/custom-fields-introduction