First, Google depends on a special object called a product feed that contains all of your store’s product data, such as titles, descriptions, images, price, etc. Google uses this data to match your products with relevant search queries as well as to create the actual ads.
On the front end, users do not see the feed. Instead, they will see the Shopping Ads, showing an image of the product, with the price and additional information, such as reviews or free shipping.
If someone likes what they see, they click on your ad which will take them to your website and Google charges you for that click.