Mule applications are composed of single or multiple connected flows that accept messages from sources like files or APIs. The messages then pass through various processors that transform, enrich, filter, and process the data. Mule applications are written in XML and deployed to a Mule runtime server, where they handle concurrent requests. The runtime enforces API policies and acts as a message bus between applications. Developers use Anypoint Studio to visually create, test, and deploy Mule applications to on-premise or cloud environments using built-in connectors. Mule APIs can also be designed with RAML and published through Anypoint for public or private use.