Not working with TwentyThirteen template

I have activated the plugin and inserted the code from the readme.txt file into the Category.php template, where it is not working nor did it work in functions.php. I am using the Twenty Thirteen theme on this blog and cannot seem to find the specified function or category/term, though categories are enabled and the plugin has enabled the selection of a category image on the dashboard and it is showing the selected image on the category settings on the dashboard. I have not altered the code you provided in the readme in any way. Please provide a solution asap.