The difference between Search Engine Optimisation and Pay-Per-Click (PPC) is that the traffic generated by SEO is organic and free, whereas PPC isn’t free. As the name suggests, you have to pay a fee per click.
In simple terms, with SEO you can get your online presence in the top positions by making sure it’s correctly optimised for a search engine. With PPC you can get a first-page position by paying for each click, which can be quite expensive.