To make the cloud shape, we're simply going to apply the second polish in three strokes. Start each stroke by placing the tip of the brush on the surface and wait a little till enough polish has dripped off forming a round starting point. Start on one side of the nail and make each stroke shorter than the one before.
Tip: If your polish comes with a (big) flat brush, just twist it 90° and use the side. Now it's easier to make those round edges! ;-)