What's the use?
This feed allows you to create ads, that include products viewed by Internet users on your website and to display those ads on other websites thanks to Google options.
In addition to providing a streamlined setup process, responsive ads may help improve overall performance of dynamic remarketing campaigns.
This option is available for all sectors, except for the retail. If you want to create a remarketing campaign for products, use the Google Display Ads.
How to display my retargeting dynamics ads online?
Its setting is similar to Google Shopping channel (Google Shopping/Online Products guide only available as pdf file), except there is no Categories Matching to do.
This feed is working through CSV and has to be registered in your Merchant Center.
To know more about its use within Google, please consult their help center.