I am not sure that I understand the question, but :
1 - to display custom meta data you do not need a hook, but a function.
it is called is get_post_meta() (click the link to learn more.)
2 - If you want to create a link , usually what is done is to have 2 meta fields, One for the URL itself and one for the URL Display text ( or your button) .
Then you cann do , for example :
$my_URL = get_post_meta($post_id, $my_URL, true); ?> $my_URL_mask = get_post_meta($post_id, $my_URL_mask, true); ?>
<a href="<? echo $my_URL; ?>" rel="whatever" title = "go to <?echo $my_URL;?>" alt="<?php echo $my_URL; ?>" /> <? echo $my_URL_mask ?> </a>
Now , if your custom fields values will be for example :
$my_URL = 'CLICK HERE'; $my_URL = 'http://codex.wordpress.org/Function_Reference/get_post_meta';
That will create you a link text link that will be like the one above .
If you do not want the url mask, and only the URL to display as text - then just use one value .
3 - If you want it to show in a BUTTON , that is a nother story, and it is CSS related - it will depend how you want your button to look, and in that case - you just put those values inside the markup.