What do the apps do?

I have created an account and received a user code that I can use in association with IP addresses for DNS servers. This works fine on PC and on Android phone. 

On the PC, I downloaded ann app that sits in the system tray. If I enable it, then I lose internet connectivity completely, so I am not sure what it is for. If I disable it, the IP addresses for the NextDNS DNS servers work fine.

On the Android phone, I entered the Private DNS address provided by NextDNS and run the app called NextDNS. If the app is enabled, then the internet connection is lost.

In both cases, I am scratching my head trying to figure out what the app provides. Does anyone know about the purpose of the apps - do they add anything?

Finally, it seems community discussions are the only source of help. Is there any support for technical issues available from NextDNS, rather than other customers doing their job for them?