The world of SEO is complex, but most people can easily understand the basics. Even a small amount of knowledge can make a big difference. Free SEO education is widely available on the web, including in guides like this. Combine this with a little practice and you are well on your way to becoming a guru.
Depending on your time commitment, your willingness to learn, and the complexity of your website(s), you may decide you need an expert to handle things for you. Firms that practice SEO can vary; some have a highly specialized focus, while others take a broader and more general approach.
In any case, it's good to have a firm grasp of the core concepts