The main difference between PPC (pay per click) & Organic SEO (search engine optimization) is the process of landing users to your website. In PPC model, It is a paid techniques and Advertiser pay to Publisher when ads gets clicked. So, we can say that payment is made per click. While Organic seo is totally different form PPC model. There are 2 main practices of SEO are On page & Off page and both are free practices to increase traffic to your website.