There are many search engines found on the Internet. Each has their own way to search for information. A bulletin board is a site you visit on the Internet to read and post messages of a particular interest to you. There are many bulletin boards that can be reached on the Internet. Each has their own topics of interest.
Bulletin boards are electronic means of communicating that have been around for a long time.
They are sometimes called forums. Classified ads on the internet are very similar to classified ads in newspapers. These sites contain various kinds of classified ads for all sorts of things. Each site has its own format and style. Directories are special sites of the internet that contain categorized links to various places on the internet.