Editing Single.php

Hi Rikard. Thank you for helping. I’ve tried to open up the Single.php file or loop-index.php files and add things as basic as a span with some text in it, but it never appears on the single post page on the frontend correctly. To confirm, I did a view page source and searched for the text I entered, but don’t see it.

Ultimately I would like to be able to add a conditional do_shortcode statement, like:

if category is named blue, show form 1
if category is named red, show form 2
if category is named green, show form 3,
and so on.

Thank you. Hopefully this helps.