Prepare the cake mix box as directed on the box's back. After letting the cake cool for at least fifteen minutes, pierce it with a toothpick, fork, or the end of a wooden spoon, about every half an inch.
Next, prepare Jell-O by following the instructions on the package, using both hot and cold water.
Cover the top of your cake with jello by slowly pouring or spooning it on.
After the cake has chilled for three to four hours to solidify, spread the whipped topping over it and garnish with any fruit, if using. Store in the fridge to cool down. Have fun!