Move Ben with your mouse so he can take header shots into the goal. I'm not lying here, the goalkeeper is really fast and will probably catch the ball the moment you start the game, so if you don't have quick reflexes, this is not the game for you (but you can still try!).
I was flicking through a bunch of tutorials when I noticed a header shot game as an example, so I actually followed the tutorial (I know!) and adapted it slighty.