Click on Play Now and then on the yellow play button. You'll be asked to choose a country (by flag), click on a flag and then on the gray button appearing underneath it. Then choose the right gray button in the next screen and then again to begin.
When the game begins and you are the kicker, you'll first have to decide on the horizontal direction of the ball (the first moving ball to the left), then how high it will be (second ball) and how strong the kick will be (the third ball). You select each of them with a mouse click or your finger to the touch screen.
When you are the goalie, you will have a split second to see where the kick will go (sign of hands) and you'll have to click on it in time to stop the ball!