Display a static content section on category pages

When a visitor clicks on a category, I want to have a little post/section above all the posts, even when the content gets updated…so that whenever they click a category, that static post/section comes before the posts of that category. I’ve worked at it for a while now w/no success. What do I do here? I imagine there has got to be a plugin or something, but I have had no success. Please help!