Add Category Display to Each Post

Hi,

I am using a theme, and this theme does not show the category a post is posted under. I do have the links for the categories to the side, and when I click on them, the proper posts do come up. I was hoping to get a category to display next to each entry, so people could see it. What is the code to do this? I think there is a custom function for this.

Thanks in advance for any help.