From the "Quick Start" doc :
You strike the ball when "Shift", "Ctrl", or "Shift"+"Ctrl" keys are hold down.
==>> You must maintain the button(s) pressed when you strike the ball <<==
If you don't press down any key, you'll strike weakly the ball.
When you hold down "Shift" and "Ctrl" at the same time, you hit strongly the ball: it's a super shot!
When you hold down "Shift" or/and "Ctrl", you can give a direction to your shot:
* push left arrow to send the ball to the left: the more time, the more to the left.
* push right arrow to send the ball to the right: the more time, the more to the right.
PS: sorry for the delay to answer. I don't know why, but your message was not flagged as unread, so I didn't notice it...