Check the Key Preferences menu item in the Game menu to see which keys do what. If the "caps lock" key is down you can use the mouse to control the putter.
When you think the putter is positioned correctly, use the swing key (or the mouse button when the "caps lock" key is down) to hit the ball. Hold it down to draw the putter back. When you let go of the swing key the putter moves forward to hit the ball. The further you draw the putter back the harder you hit the ball. If the putter reaches its maximum backswing position it automatically begins its stroke.
