Your brain is a very important part of what is you. Your brain (you) has been programming itself from your experiences and actions since you were born and it is still doing it now. The more you do (and learn) the more you will become.
Because our experiences are all different, we are all different and we have different opinions and want different things.
Interestingly, activities such as ‘marketing’ are attempts by some people to make everyone else think a certain way and some of them are very good at it. They are particularly good at telling younger people what it is they want but they can also influence older people too.
Free will is an interesting concept. It is something which we all mostly think we have but on reflection, is rarely complete. Why do we all want a particular phone or want a particular brand of trainers? Have we all just reached the same logical conclusion or is there something else at work?
Asking, who am I, is a good question but it is not so easy to answer. Try reading some basic philosophy because that is where you will find lots of well constructed arguments which relate to who you are. But don’t expect answers, just interesting questions.