The Element Layout is a widget group what allows you to arrange information on a task page or an app form in the most convenient and user-friendly way.
For example, by using tabs and panels you can group associated data and divide forms into logical segments. Thus, it will be easier for a user to find information on the app form or to correctly perform a task.
You can place other widgets and variables from the properties tab (only for forms) within the Element Layout widgets. Read more about variables in this article.
Read more about the widget configuration in the following articles: