There are a number of different courses that can be taken up online. These courses can teach you the fundamentals of seo and how you can further implement and apply that knowledge to your own websites and pages. One such course is seo fundamentals from google digital garage created by university of California. There are no prerequisites required, just the right kind of dedication. Sites such as Coursera also offer courses related to seo and marketing, which have a test and can be done by anyone who takes a keen interest in the topic and studies the course well. After that you can also apply your knowledge to your own website or maybe also provide your services for a fee and earn.