It returns to web pages at certain intervals, in order to index new material. When you use a search engine, you are asking it to look in its index to find matches with the words you have typed in. Some search engines index not only the World Wide Web, but also Usenet newsgroups. Many search engines are now becoming reference sites which contain much more than just search capability. They may also have news, weather, free software, picture indexes, ratings of web sites, and other features.
Search engines present their contents in two basic ways.
First, many of them contain large indexes of every word found on every web page indexed. You can find pages that contain the words you type in by using a word search. Second, many engines also present their contents in the form of subject directories, allowing you to find a topic by clicking through several levels from the more general to the more specific. There are several ways to type in a word search. Knowing the differences can help you get better results.