The advantage of a search engine is that it will return a listing of every single document that contains your search terms. The disadvantage is it often produces thousands of listings, many of which are irrelevant. Two popular search engines are Excite and Alta Vista.
Directories organize their listings according to subject, and are maintained by human beings.
Yahoo, arguably the most well known search site on the Web, is a directory. A third type of search tool is called a metasearch engine, which utilizes a number of other search tools to compile a comprehensive list. This type of search is slower, but the results can be very thorough. Dogpile is one such metasearch engine that lets you choose which search tools it will access. Take some time to explore the different sites.