First apply a base coat to protect your nails and let it dry. Then apply a mask (this is a product you can buy it on a beauty shop or you can even use liquid latex which is exactly what it is). This is used to avoid messy edges while doing artistic nails such as these ones.
Now take a latex sponge and paint stripes with your chosen nail polishes to one of the sponge's edges. Be generous.
Apply the mis with the sponge and little and gentle touches. You may need a second layer.
Before it is completely dry remove the mask. And if its needed remove the excess with a pencil brush wet with polish remover.