How do the Search Engines find websites?

[smmexpertss]

Search engines are the key to finding specific information on the vast expanse of the World Wide Web. Without sophisticated search engines, it would be virtually impossible to locate anything on the Web without knowing a specific URL. But do you know how search engines work? And do you know what makes some search engines more effective than others?
When people use the term search engine in relation to the Web, they are usually referring to the actual search forms that searches through databases of HTML documents, initially gathered by a robot.