what is seo services ? is it necessary for website ?

http://bit.ly/wixpa seo service provider utilizes the practice of search engine optimization to increase the amount of visitors to a Web site by obtaining high-ranking placements in the search results page of search engines (SERP). Typically, a business will hire a service provider to improve its organic Google search result listings.
SEO services help to ensure that a site is accessible to a search engine and improves the chances that the site will be found and ranked highly by the search engine. SEO service providers offer a wide range of packages and options for search engine optimization, ranging from one-time fees for smaller sites to monthly subscriptions for ongoing SEO efforts and support.