Advanced Custom Fields allows adding custom fields (also called metadata) to your WordPress site.
Visual Composer provides the Advanced Custom Fields element which can be downloaded from the Visual Composer Hub. The element allows displaying custom fields from the Advanced Custom Fields.
As a developer, you can also add an extra class name to the element and use local or global CSS to style the output of your field to your liking.
In addition to that, Visual Composer offers Dynamic Content Fields feature which allows you to use custom fields from Advanced Custom Fields.