Understanding MVVM Architecture in iOS

I have few questions in order to understand the MVVM architecture for ios as below -

1. How Is Model different from the view-model? The model also has the data and why do we need to write and update the same properties in view-model (Repetitive code)?
2. Creating two-way data binding between view and view-model can be good in form validation. Any other application except it?
3. Should we use KVO to create 2 binding between view and view-model? Any disadvantages anyone experience so far?
4. Should we put Networking(API data fetch) Code inside view-model?