Getting the category to show in the post

I want to show the category of each post in the post content, and am sure there is an easy way, but can’t find it again.

I am using TDO Mini Forms for people to create posts, and I can add an append post widget using code such as:

<?php
?>

But I can’t work out what I need to put in there, to get the category name to appear.

I feel it should be so simple, and that I may be missing the obvious, but I have sat trying this for the last 2 hours.