Free will simply means that we make our own decisions about what to do, based on our desires and beliefs. We would lack free will if external circumstances, such as fate, determined what we do.
This is according to compatibilist theories of free will.
If compatibilist free will were an illusion and not real, we would expect people that what people do and what people say they wanted to do would only coincide randomly, because saying things is also a choice.
Nothing is random. But because everything acts according to laws, and when all the variables and laws are known then it can be predicted with a 100% certainty, which means it is predetermined which means that there is no such thing as free will but only fate.
You are only doing that because you are here and someone posted this thread and you believe in free will, choosing to support your theory as if you had free will when you cannot prove that.