Organic SEO is different than PPC SEO. In pay-per-click search engine optimisation you pay for the clicks and for every visitor that enter on your website.
Organic is the best traffic ever , because it`s natural , no spam and it`s the easiest way to get real customers. The difference is that the search engine users , that are looking for something , if they can find that informations or services in your website , you will have a better rank , so more chances to be visited by potential customers. Let them find you!!