How do I add an App to an on-premise SharePoint system?

This requires 2 separate actions because the App will use a different url (e.g. sp2016-xyz12345.yourcompany.com) to support your SharePoint system (e.g. sp2016.yourcompany.com).

First, configure your DNS system with a "forward lookup zone". See https://www.enjoysharepoint.com/configure-on-premise-environment-for-apps-in-sharepoint-2016/ for further details.

Secondly, add the App to your App catalog. See https://www.enjoysharepoint.com/create-app-catalog-site-in-sharepoint-2013/