How can I create a catalog of one category of posts?

We contracted with a local firm to develop our site, http://www.firstparishbeverly.org. On Minister’s Page</strong, clicking button Previous Letters brings you to a very long page of all posts from this category. Past Sermons acts similarly. I would like Previous Lettersto bring up a listing of those post titles & publish dates grouped by Month and Year, in other words a catalog of Letters. How do I do this?