SEO is applicable to all the search engines whereas Google Adwords is applicable to Google sites.
SEO is a slow strategy that takes time to show results and the traffic generated is organic.  whereas, Adwords traffic is paid and shows immediate results. Since Adwords generates paid traffic once you stop the payments the traffic is also stopped, but in case of SEO once you start achieving ranks in SERP the traffic keeps coming. To get SEO results you constantly need to work on the website so that it can rank better, whereas with PPC you work on the Ads to generate traffic on the website.
Even though they are different strategies SEO and PPC but they do work together to generate amazing results.