I suppose you are asking about craiglist. Craiglist is the best classified directory where one can submit his ads describing about his services and products and could promote his services region wise.
A classified site is a place where you can place your advertisement to promote and announce your services/products and etc.. You can place ads for promoting your services and to make your site/services reachable for people who are looking for the same services or products you are selling/offering. Hope this helps!