wrap excerpt around thumbnail in child theme

I have recently installed a child theme and want to wrap the text of my excerpts around the thumbnail featured image in my category pages.

I used this forum for advice last time

But here deepbevel talks about editing my loop.php and I’m not sure if/how I need to add one to my child theme?!

At the moment I only have a style.css in my child theme, and haven’t yet added functions.php.

Can anyone tell if I should be adding more files to my child theme, and which ones to edit the way the text is displayed/wrapped in my category pages?

If I can just follow the original advice of deepbevel in the link above, should I be adding a loop.php to my child theme?

thanks!!