There are 2 types of search engine optimization: on-page and off-site. The on-page seo means that your website should have a specific structure to be better indexed by the search engines. Also, you should follow the best practices in order not to be penalized.
Supravirtual (the company I am representing) offer only on-page SEO, that meaning we'll analyze your site, its structure and its content, we'll correct the errors (if there are any) and we'll offer you advices about the current best practices online (the things are constantly changing but we follow the news in the field).