Get Wordpress Category from Single Post

For the lazy and the learning, to put it into your theme, Rfvgyhn's full code

<?php $category = get_the_category();
$firstCategory = $category[0]->cat_name; echo $firstCategory;?>

How about get_the_category?

You can then do

$category = get_the_category();
$firstCategory = $category[0]->cat_name;