Why can't I control what my brain does? Where does the line that divides my mind from my brain starts? If, for example, my brain is producing hormones from the hippocampus why can't I stop them if I want to?

I am supposed to be my brain, my mind, at least more than my body, people can describe the body just as a bag of flesh that allows us to live, but what can't we control everything what the brain does? Where the part of the brain that is not my mind but just another physical organ of my "bag of flesh" starts? What parts of the brain are actually me then?

How does this combination of software and hardware works? Please, I need to know.