Your starting point is not good at all, STT. I insist that we need to start with the analysis of our experience. That way, perhaps you would be able to understand the meaning of certain philosophical terms. When you say “you have mind and brain”, it seems as if you thought that I am a thing that possesses at least two other things: mind and brain; which is a rather crude way of thinking.
The analysis of my experience shows me that I belong to the realm of interactions, and that I also belong to the realm of relations. It also shows me that relations and interactions are irreducible to each other.
It is because I am corporeal (including the fact that a brain is an aspect of my corporeality) that I participate in interactions. And the fact that I am a being able to establish relations is what I mean when I say that I am a mind, or that understanding is one of my faculties, or that I am spiritual. Once here, I can respond to your crude question in the same fashion: my brain interacts; my mind establishes relations.