The government has made it mandatory to download the app only for government workers and employees of private food delivery services. I have not downloaded the app, and I have not been arrested or fined. The government just wants to encourage everyone with a smartphone to download the 'Aarogya Setu' app; it has no power to make the use of the app compulsory without legislative consent.
While the government initially claimed that the use of the app would be purely voluntary, it soon made it mandatory to download the app for government workers, but the use of the app for normal people is more or less voluntary.
A coupe of days ago, I helped my mom configure the app. All it asks for is your age, gender, travel history, and symptoms. The app shows a message if you are in "moderate" or "high-risk" which is based on your proximity to a contacted person who has tested positive for the virus. You just have to keep your location sharing to 'always' and the app sends your location data to the government. Once the epidemic is over, the users can delete the app.