Currently i reading in official google doc news about Android 7.0  

I can not understand a few things.
They wrote Doze improve battery life by turn off network and CPU when user block the screen.
But how this works ?

1.I have Marshmallow in my device, and when my phone is blocked, i still get notifications from app with network (e.g. Messenger).

2.Second thing they wrote Nougat have improved this more by again CPU and network. So what is exacly differet ?