That is a great question. I've been doing SEO more than 6 years. There are two factors in SEO. On-Site SEO and Off-Site SEO. On-site SEO is a techniques that includes adjusting the layout of your website, adding code on pages, HTML scripts, inserting relevant keywords within the content of your website. These edits have a direct influence on how your website behaves in search engines. It is the foundation of your website’s SEO and it accounts for around 30% of your website. Off-site optimization techniques include mant tactics and of the the processes is "link building" or getting links back to your webpages from others. It refers to things that happen away from your website that can influence how your website behaves in search engines. It accounts for roughly 70% of your website’s SEO strategy. But with Google's update, more emphasis will be on high valuable content and social media signals. Here is a great resource for beginners http://moz.com/learn/seo If you have any more questions, just let me know