Search engine optimization specialist tweak your web site in order to deliver more traffic. They all have their own methods but most commonly they will analyze your web site content and HTML Meta-Tags for best performance. By choosing specific keywords for your search terms, they will work to get your site listed as high as possible in the search engines. Make sure you research the company well as some SEO companies can actually hurt your traffic if they violate the rules of search engines! Be sure to check references of clients that have used them for at least 6 months.
Search engine marketing professionals all have different pricing structures and cover a wide range of pricing and service. Make sure you have defined the requirements for your web project and both of you have an understanding in writing of what is expected.