Databus is just an MQTT broker so you need a client on your application side.
I would suggest creating a new user in Databus (using the Databus configurator) for you app with access rights to a topic of choice (where you want to publish or subscribe data from)

Using these user details you should then be able to connect to the databus

Of course you will need to build in an MQTT client into your application but you should be able to find plenty libraries for the language of your choice. Paho could be an example.