Individual search engines use complex algorithms based on a site's information and html code to rank sites. Google is an example of a pure search engine site. Directories are the second type of search site. To get listed on a directory, you must actually submit your front page on the directory's submission form. Unlike pure search engines, directories don't automatically add sites.
Human reviewers check every submission to decide if it's appropriate for the directory.
Web sites submitted to directories are usually ranked according to the information provided on the submission form, as opposed to actual information on the Web site, so what goes on the form is critically important. The Open Directory is an example of an Internet directory. Most of the major search sites on the Internet today combine search engine and directory functionality. Major search engines like AltaVista, Excite, Lycos, HotBot, and Infoseek all have some form of directory associated with them. If no results from their human-edited directories match your search query, their search engines then search through a database of spidered sites to give you results.