The body/mind/brain, evolved to respond to its environment generates behaviour, thoughts, feelings, will, and puts needs and wants into action. You feel the need for something and you act. The brain is forming and generating you, your needs and wants and your actions. Which is the evolved function of life. To respond, to survive, to procreate, to act.
Do some research into basic biology and neuroscience. I shouldn't have to spoon feed you with basic information.
