Benjamin Libet carried out experiments to try to understand the nature of intentionality and motor action. What he did was to monitor the subject's brain in that region responsible for initiating action. The subject watches a clock on a computer screen. He is asked to press either button A or button B whenever he is ready and to note the time on the clock when he makes the conscious decision. The computer subsequently records the time verbally claimed for the decision and compares it with the time automatically recorded when the brain triggered the movement in the hand to press the button. The interesting thing is that the claimed decision to press a button always takes place after the brain starts to move the hand. Irrespective of whether or not this proves anything, our experience is effectively what we mean by the term free will.
If what Libet concluded is true, however, what it means is that this 'feeling' of having free will is only a 'side effect' arising in the brain after some action has been initiated in automatic response to a combination of stimuli.