PPC and SEO are two different things. Here’s the difference:
PPC (Pay-Per-Click) - This method involves money. You market your products and services for which you pay some amount for every click you receive (CPC), every 1000 impressions you get (CPM) or evry conversion you acheive (CPA). Also, you use certain platforms such as Googe Adwords, Facebook Paid Marketing, Twitter Paid Marketing, LinkedIn Paid Marketing and more to advertise your products and services.
SEO (Search Engine Optimization) - SEO results in visibility of your products and services in organic listing on search engines. Search engines do not charge for this service. Instead, they have certain algorithms in place which your website needs to comply with in order to achieve good ranking. Broadly, SEO techniques involve writing original content with relevant keywords, user experience on your website, page load time, traffic quality and many more factors.
In case you handle SEO work to an agency, they may charge you for the services they offer but you do not pay to the search engines directly.