Click on the small play button (on the blue bottle).
Now, click on the level the game takes you to (a colored gem with a number on it). An arrow will show you where to click.
At the start of each level, you will be give a number of moves you are allowed to use, and the target you need to reach in points before using them all.
To play, use your mouse cursor or your finger to move any gem you want one space, either horizontally or vertically, to create a series of 3 or more gems of the same color. Once you do, they will disappear and give you points towards your goal!