Searching is not evaluating. Given the nature of web information, it's vital to evaluate the web pages you dig up. See Evaluating Resources for things to consider when evaluating a web page. Because the web is so large and changes so fast, the search engines' databases are always incomplete and out of date. The robot should revisit the page periodically to look for updates.
Indexing software builds a database out of all the words the robot recorded.
Finally, when you try a search, the search engine's search software looks through the database for the keywords you entered, and then ranks the matches using a ranking algorithm. Generally, the advantage of using a search tool over a metasearch tool is that you can take advantage of features specific to a particular search tool to enhance the precision of your search. In addition to using an algorithms like other search tools, Google analyzes hyperlinks or sites linking to a particular site, thus relying on the collective expertise of other sites to determine the relative worth of a site. The relatively simple no-frills interface makes searching easy. A comprehensive search engine for more than 150 million Web sites that is best for the beginner.