A search engine sends a spider which is also known as bot sometimes to crawl the servers on the world wide web to find data to bring back to its index or database. In the index, it filters documents according to the search engine’s rules and stores those which meet its quality criteria.When a searcher makes a request, the search engine evaluates the sites in its index, assessing which are the most relevant to the requested information, based on area of expertise as evidenced by keywords in content, and references in the form of links from authoritative sites. The links that count with search engines are the ones pointing to your site.

SEO can be helpful to Search Engines in these ways……

• It addresses the limitations of the “bots” with crawler-friendly site architecture, as well as addressing indexing filter issues.
• It makes the site accessible to searchers by identifying keywords most used by the target audience and writing the keywords — sensibly — into the text of the website.
• It attracts inbound links from authoritative sites and targeting those links to searchers’ interests.
• It analyzes visitor activity on the site to look for ways to improve the search experience for both.