Search engines use automated software programs knows as spiders or bots to survey the Web and build their databases. Web documents are retrieved by these programs and analyzed. Data collected from each web page are then added to the search engine index. When you enter a query at a search engine site, your input is checked against the search engine's index of all the web pages it has analyzed. The best urls are then returned to you as hits, ranked in order with the best results at the top.

search engines example : Google, Yahoo, Live Search, Ask and Altavista.

The search engines major factor in the arrival of visitors to your site by focusing on your Keyword or Key phrase, which help users to find your site, and thus your site from sites that serve the users on these words, there are some tools for helping the Webmaster to analyze the site and supervised by a redirect visitors to the site to ensure easy access it.

This site offering a free tools you can use them.