For the clouds, all you need is white nail polish. Begin by cleaning off your brush of all excess polish so there's barely anything there. Stoned said this is the best way to be in control of the brush. Then, simply blob on little white dots clustered together to create a cloud. Depending on how big your nail is — Cyrus remarked that she has "baby nails" — you'll be able to fit anywhere from two to four clouds.
Pro tip: using this same tutorial but with black and white nail polish, you can create a cow print nail art design.