Each search engine looks for the occurences of the words you enter in its list of websites. A search engine does not search the whole Internet, only the sites that have been registered with it. Other search engines offer premium contents for a fee. Also, most search engines often have a help section explaining how to narrow down your searches.
Subject guides involve people who select and review websites.
They are organized by topics, going from broad to specific. The subject categories can follow standardized schemes, like the Dewey Decimal Classification, or they can be original in-house systems. Most of these guides offer keyword search capabilities. It is the closest you will ever get to be able to search the whole Internet. Metasearch engine will often offer various search possibilities, like searching discussion lists archives or browse subject guides.