keywords and description

I know I am going to sound stupid to the bone, but how can I get keywords and descriptions in the header?

I tried to add a custom tag for a post and a page then used the Custom Fields, but whenever I use the Loop the words show up, but the posts crash – e.g. I get the “Sorry, no posts matched your criteria”.

here is my code
`
<?php if ( $posts ) : foreach ( $posts as $post ) : start_wp(); ?>
<?php the_meta(); ?>
<?php endforeach; else: ?>
<p><?php _e(‘Sorry, no posts matched your criteria.’); ?></p>
<?php endif; ?>`

TIA