Searchengines are software programs known as crawlers, spiders or robots. A robot is a software that automatically follows hyperlinks from one document to the other around the Internet. When a robot discovers a new site, it sends information back to its main site to be indexed. Because Web documents are one of the least static forms of publishing, robots also update previously catalogued sites. How quickly and comprehensively they carry out these tasks varies from one search engine to the next.
Search engines use software robots to survey the Web and build their databases.
Web documents are retrieved and indexed. When you enter a query at a search engine website, your input is checked against the search engine's keyword indices. The best matches are then returned to you as hits. Keyword searching This is the most common form of text search on the Web. Most search engines do their text query and retrieval using keywords.