How to add description to Category?

If I click on a Main Category, such as, Shirts... that will then show a page that lists the sub-categories.

I would like to instead go to a custom description of the overall category, rather than listing the sub-categories.

Any ideas?

You can include as much description as you want in the category editing page in admin > Catalog > Categories/Products > edit category.

To hide the subcats listing, add to your stylesheet

.categoryListBoxContents {display: none;}

This will work on all categories; if you want it to apply to only certain categories, you will need a category-specific class/id tag somewhere to narrow the specificity.
Smart Backgrounds can be used to get these class tags, if you want; or you can use category-specific stylesheets with just that rule in them.