How it Works
Search engines, such as Google, Yahoo!, and Bing, scour the World Wide Web. Their automated "robots" (also called "spiders") move from page to page and site to site by following links. Along the way the read the code for the pages they visit. The information from the page code is incorporated into the search engine's vast knowledge base.
When a visitor to a search engine enters a term or phrase into the search box the term or phrase is compared to the information in the engine's knowledge base. The results that are returned (called "organic results") are listed in order of how well they match the term or phrase that was used to initiate the search.
The comparison is accomplished by algorithms. The specifics of the algorithms are closely guarded secrets of the search engines. Apparently, the algorithms vary from search engine to search engine. However, the techniques that we discuss here are applicable to all the engines.
The closer the Web site matches the search term, as determined by the algorithm, the higher it will appear in the list of organic results. The goal of search engine optimization is to help the Web site and its pages rank as high as possible in these organic results.
It is important to remember that search engines sell advertising on their sites. Which ads appear on the results page are also determined by sophisticated algorithms, and are based on the comparisons with the search terms. Your organic result placement will compete with these ads. The better your search engine optimization, the better your placement in the overall results.