Product listing ads are a powerful ad format available through Google which allows retailers to showcase merchandise through images on Google.com. Because users can already see what the products look like and how much they cost, it's an extremely effective and profitable way to advertise with often better conversion rates than your standard text ads.
You'll need to have an account and a data feed submitted with Google's Merchant Center. The Merchant Center allows retailers to submit products, which show on Google Shopping, Product Listing Ads, and on Google Commerce. If you do not have a Merchant Center account, you can get started at www.google.com/merchants.
You'll need to create, upload, and regularly update a formatted feed with all of your products. There are feed management companies that specialize in creating and optimizing your feeds, including http://godatafeed.com/ and https://www.singlefeed.com.