Search engines are programs that maintain large information databases.
These databases can be searched by keyword(s) or subjects.
They return a list of links to, what one hopes are, relevant pages.
Yahoo - pages examined and categorized manually
AltaVista - automatic keyword extraction
* - In general, providers MUST request that their pages be included in these databases. Therefore no one indexes every single web page.
* - Search engines use different ways of building indexes. What works for you on one engine may not work well on another.
* - Getting obsolete pages deleted is difficult. Many links do not work or have other errors.