In the video, a woman is seen decorating a cupcake with a rainbow-colored fondant. She starts by placing a black fondant circle on top of the cupcake, followed by a red fondant strip, then a yellow strip, a green strip, and finally a blue strip to complete the rainbow. The woman uses a spatula to smooth out the fondant and ensure it adheres properly to the cupcake. The cupcake is placed on a wooden surface, and there is a glass of water visible in the background.