The web's language is HTML. Every page rendered by a web browser has some HTML content. Therefore, the ultimate job of any website is to generate the HTML that contains data formatted in the desired manner. The browser then renders it and hopefully displays something beautiful, informative, and useful.
Knowledge of HTML is ubiquitous in the Web Design world. There are many resources, including books, online courses, and other tutorials, that will teach you the basics of building a web page.
The Mozilla Developer Network (MDN), which can be found at https://developer.mozilla.org/, is a great place to start.
ServiceNow uses Jelly to generate HTML. The Jelly processor in ServiceNow takes in an XML template and produces ...