You will need...
... Pink & green nail polish
... Black sharpie
... Top coat (transparent, obviously)
Cut your sponge into a small (about 1 x 1 inches) piece and apply the colors as shown..
Put it carefully on your nails creating the ombre effect.
Let it dry completely and draw rain drop formed dots on the pink side of your nails. Apply your top coat.
Remove the owerdrawn polish from your fingers using a Q-tip and nail polish remover.