SEO involves optimizing websites to achieve high search engine rankings for key phrases. It can be divided into on-page optimization of HTML, content, and site structure, and off-page optimization like building links. Doing SEO properly entails optimizing the site for both users and search engines to provide a good user experience while getting indexed and ranked well by search engines. Regularly adding fresh, valuable content encourages search engines to crawl the site more and recognize it as authoritative. Black-hat techniques aim to manipulate rankings and should be avoided.