You have a canvas where you can weave: choose the colored yarn ideal for each situation and go to the end! Your goal is to wave the complete canvas, but you don't have too much time. It takes practice!
To chose the color of the yarn, click on the corresponding skein. Use the arrow keys left/right to move the knitting needle for weaving. If you apply the right color, it will show in the canvas; if not, it will be visible as a red cross, and you'll have to restart. When you reach a border, you go up a line by knitting in the same direction, and then you have to inverse it to advance in the opposite direction. The space bar is useful to go faster, because it switches the yarn color to the one you used before the current one.