This campaign type doesn’t provide a new ad format but rather a different kind of campaign management where you leave a lot of the work to Google’s algorithms. You essentially provide some data input from which Google figures out who to target, what to bid on, etc.
This is what Google says about Smart campaigns:
Smart campaigns are Google’s efficient, easy solution for small businesses and helps your business get discovered on Google in those relevant moments. Powered by the best of Google’s advertising technology, Smart campaigns bring you results based on your campaign goal, whether that be customer calls, visits to your location, or actions on your website.