The Windmill is a neat pattern for two reasons, its fast, and it’s required for Mills Mess. It can be tricky however, because it requires crossed arms. The easiest way to think about the Windmill is a repetition of throwing underneath your arm, and throwing above it; and the throws should all look exactly the same.
Start with 2 balls in your right hand, and one in your left. Take your right arm, reachunderneath your left, and make a throw back towards the right side. Follow that throw with a throw from your left arm, which should still be above your right, again throwing towards the right. Finish the pattern by making the first underneath throw again, and repeat as necessary.