So I found that I didn't have to enable the thumbnail code in the functions.php, that WordPress already buried the command in a subfolder. However, I would like to make some changes to the thumbnails that appears on the main page. I assume I am looking for something like
<?php if(function_exists('has_post_thumbnail') && has_post_thumbnail()) but I can't find it in the loop, single loop, or attachment php files. WHERE is it?