Google Shopping is described best as a paid comparison site. Google Shopping displays its results in a separate section of Google's search engine, but also in organic, non-paid search results. Because it also displays images of your products, these results attract attention.
SEOshop offers the possibility to place your products in Google Shopping. This is done through a Google Product Feed. You will have to create a Google Shopping campaign in Google AdWords. Google Shopping works on a pay-per-click basis, you only pay if someone clicks your ad and is taken to your online store. If you want to create ads with product listings, you will need an AdWords and Merchant Center account.