One way to understand free will is to realize that "we are our genes". Our genes define our wants and motivations -- they are not something that we have; they are something that we are.
In other words, I am someone who is defined by 20,000 gene variants, like an identity card. Some subset of those gene variants can predict my personality, including what choices I will generally make in most situations.
For example, if you are an INTP personality type, you won't want to lead or control people. That will be your choice, based on who you are (i.e. what you genetically want). It will not be a choice based on free will, unless you define free will as "doing what you genetically want". Your genes define who you are, and your choices are based on who you are.