I’m trying to figure out how a Service Manager and a Device Handler communicates. I’ve seen some parent.CallMethod examples but I don’t understand what that is.
I’d recommend giving these a read over. They should definitely clear things up for you 
http://docs.smartthings.com/en/latest/cloud-and-lan-connected-device-types-developers-guide/building-cloud-connected-device-types/building-the-device-type.html?highlight=parent