The aim of search engine optimisation techniques is to display your website listing high in the organic (free) results pages from search engines like Google™ or Yahoo!
The free listings are ranked according to the relevance of the website according to the search terms entered by the user, and attract the most traffic.
The paid listings are optional and are charged to you each time someone clicks on the link to
your website.
The image below shows free listings outlined in green, and paid listings outlined in blue.