I was looking for the best way to pass entry parameters (username, password) to Xamarin MVVM viewmodel by clicking a button(in the view) with command parameters.
This repo might be helpful for you
https://github.com/deanilvincent/Xamarin-Forms-Simple-MVVM-Login
If you're new to MVVM in xamarin forms, this link might be helpful for you as well.
Basic Understanding How Data Binding and MVVM works in Xamarin Forms