Paint your nails with a base color and let them dry completely. Then come back and paint a layer of another color on top, and before it dries, you dab pieces of wadded up saran wrap on top lightly, then top coat
@sondallea Paint a regular coat of dark polish all over your nail. Quickly put a few small dots of lighter polish on your nail while everything is still wet. Swirl them together to create a marble effect with either a fine brush, a toothpick or a needle.