how works e.g. function the_content ?

hi,
i try to create a field with links. it should belong to a post. when i write a post about the weather it would be cool to have links like weather.com and sunshine.xy next to the article.
i added an input field to /wp-admin/post.php and a field in the mysql table wp_posts. it´s no problem to write data in the database.
but how come data frome the database on the site?
index.php: <?php the_content(); ?>
template-functions.php line 905: function the_content(...>
but in which file is the mysql query?
thanks, oerdec//