It would seem that communication should be easy and simple, but of course it’s not. It’s often quite complex due to the many layers of messaging that are present when someone speaks. Even a single sentence can be complicated.
The first layer is the obvious one. The words. You have a thought or feeling you want to get across, and you choose the words to do that. If the subject is pretty concrete, meaning it’s about something that isn’t ambiguous or up for interpretation, then the communication’s probably quite clear.