Search engines find web resources by scanning the Internet using key words and phrases that are entered or defined as parameters. When the search is complete, a list of resources, links, related to the search appears on the screen. Each resource is a link to another site on the web that can be accessed with a click of the mouse. A search engine works much like a card catalog in a library. Since there are so many different resources available on the Internet, it is difficult to find necessary information.
Search engines update their indices, usually each night, by searching the entire Internet.
When you use a search engine you are searching what the engine has previously indexed. Keyword indexing is the most common form of indexing on the Web. Most search engines index by keyword or by key phrases. Words that are mentioned towards the top of the document and words that are repeated several times throughout the document are likely to be chosen as important. Some search engines, like AltaVista, index every word on every page.