Click on Play and as the game begins, you will need to place the shapes in such a way that makes complete rows. Each row is 10 blocks wide. Whenever you make a complete horizontal row, it will vanish, leaving room for more. You will get one shape at a time, and you can change it's orientation by using either the keyboard arrow keys or by clicking with your mouse or finger on the arrow buttons.
Clicking up or down will change the orientation of the shape, while clicking left or right will move the whole shape left or right so you can put it down where you choose.