By understanding the Google Display Network and your targeting options. Google Display ads are ads that are created through Google Adwords and over the Google Search Network. The differentiating factor is that your ads will be shown outside of search results on the millions of websites which are part of the GDN, and you can define your targeting in-market or affinity audiences, similar audiences, placement, and topic targeting.
The way you pay also depends on the whether you choose smart or manual bidding.