I consider using the Adwords Remarketing option for people who visited my website, but left it e.g. after viewing their shopping cart and eventually not bought anything. However, I wonder how does this work: If the traffic on my website is natural (no Adwords), can I use Adwords Remarketing to show my banners on other websites that these users will browse later? How will Google Adwords know who has visited my website? Also, does this work the same way with Facebook?