This is probably the most discussed pattern around MVVM, so no ignorance there at all, you're just in the same boat as us all :) In fact, there is an interesting discussion around this right now on the WPF Disciples group:
(check the latest messages in the thread). Glenn Block speaks of 6 different manners to communicate with the View.
1. INPC / Property binding
3. Messages (Event Aggregator/Messenger/RX framework)
4. Through an intermediary such as a service
5. Through an interface
6. Through delegates (View passes delegates to the VM which it can use to call it back. For example VM might expose a SetActions method which the View calls passing it delegates.
Which method you choose depends very much on your scenario and personal preferences. For myself, I rely on bindings (of course), on Messages and sometimes on one or the other of the six.