The Difference between AdWords and PLAs
Both AdWords and PLA campaigns are managed through AdWords.
Product Listing Ads are cost per click (CPC) ads which online merchants purchase through AdWords. These ads appear on Google Search pages to the left, and top of results. They feature product images and are tailored towards products and product categories.
AdWords are text ads are also CPC ads that are purchased through AdWords. They are based on keywords (not products or product categories). The ads usually have a highlighted background.
Both programs are moderated by what you bid on (adgroups for PLAs, or keywords for AdWords) and your daily budget. Both click through to your site.