adding an image as a category which would link up to a post

Hi,

I am trying to add an image to a category.

So instead of seeing the name of the link to the post -> I see an image.

Like a small thumbnail which links to the post.

https://www.gp2b.com/affect-an-image-to-categories-in-wordpress-without-plugin/

But my theme didnt have a category.php so I added the last bit of code to archive.php and added a category.php and entered in the code there.

But either it didnt work or I dont know how to do it. Cause I dont see any place where I can add an image when I create a new category.

Just would like to have an image instead of a word that links to a few of my posts.

Thanks for any help given.

Lionel