Do I need ViewModel for adding information to database?

I know we need view models for business logic.

Yes, that is correct. It's recommended to put your business logic in the ViewModel, as it should serve as the connector between our UI and the rest of your app. Besides that, bear in mind that the ViewModel it's a class that is designed to store and manage UI-related data that are lifecycle aware. It allows the data to survive configuration changes such as screen rotations.

but I have no idea about that Is it necessary when adding data to Firebase.

Yes, the read and the write operation should be managed through the ViewModel.

If it does, I can't access the views where users enter data from a ViewModel.

The views should never exist in the ViewModel class. You should only have objects that can be observed from the activity or fragment.

how to access these views from ViewModel?

It's exactly the opposite. You access (observe) the data in the ViewModel class from the activity or fragment classes. I have also written two articles that can help you understand the concept:

• How to create an Android app using multiple Firebase products in Kotlin?
• How to make a clean architecture Android app, using MVVM, Firestore, and Jetpack Compose?

While having a view model is custom and improves the readability of your code, it is not required. Instead of a view model, you can also handle all interaction with the database through Map objects and primitive data types.

If you're using Firestore, that is actually what most of the documentation does, such as in the documentation on adding all types of data. For Firebase's Realtime Database the same logic applies, although the documentation only shows examples with view model objects.