After defining responsive image styles, you can use them in the display settings for your Image fields, so that the site displays responsive images using the HTML5 picture tag. Open the Manage display page for the entity type (content type, taxonomy vocabulary, etc.) that the Image field is attached to. Choose the format Responsive image, click the Edit icon, and select one of the responsive image styles that you have created. For general information on how to manage fields and their display see the Field UI module help page. For background information about entities and fields see the Field module help page.