Search engine optimization (SEO) is the process of improving the volume and quality of traffic to a web site from search engines by a Google or Yahoo .Usually, the earlier a site is presented in the search results or the higher it "ranks", the more searchers will visit that site. SEO can also target different kinds of search, including image search, local search, and industry-specific vertical search engines

If your site is ranked high by the search engline, only then are the chances that you site will be visited for any purchase.