create a template file for your content type, in your theme folder. it should be something like
node--node_type.tpl.php . In that file you should have access to all the node's fields.
You can start by using the default
node.tpl.php as an example. More about templates you can find here.
in your default
node.tpl.php you could find something like this:
// this is taken from the omega theme
<?php if ($display_submitted): ?>
<footer class="submitted"><?php print $date; ?> -- <?php print $name; ?></footer>
<?php endif; ?>
so instead of
print $name you could do something like
print l('your custom field value', 'user/' . $node->uid)