In order to create power on your downswing, you need to 'get behind the ball' at the top of your swing. This involves rotating your shoulders and hips away from the target, so the majority of your weight shifts to the back foot at the top of the swing. Once you have wound your body up behind the ball, then you can shift your weight towards the target and fling your arms to hit the ball. Where a lot of people go wrong is they never quite get behind the ball at top of swing, so then they can't shift their weight on the downswing.

Here is a drill to help you learn how to sequence your downswing, will help you create more clubhead speed and power.

Set up in your golf posture without a golf club and simply hold your arms out as if you were holding a ball.
Make a backswing and stop at the top.
Lift your front foot off the ground so that all your weight is on the back side. Keep your head steady and maintain your balance.
Start your downswing by planting your front foot on the floor and then shift your weight towards the target and finish your swing.
Lift your back foot as you finish your swing.
Return to the start position and repeat exercise.
Do 8 to 10 repetitions.