The Structured Data Markup Helper helps you mark up elements on your web page so that Google can understand the data on the page. Once Google understands your page data more clearly, it can be presented more attractively and in new ways in Google Search. In addition if you send HTML-formatted email to your customers, Markup Helper can show you how to change your email templates so that Gmail can present the data to the user in new and useful ways.
Learn more at https://support.google.com/webmasters/answer/3069489?topic=3070267