First, bake your cake and follow all instructions on cake box (in 1 layer). Let your cake cool for about 30 minutes. Make sure to leave the cake in the pan. Next, poke about 8-10 holes in your cake with a fork. Make sure to go straight down and come back up again (this is to let Jell-O Gelatin seep into cake).
Then, you prepare your gelatin as stated on the box excluding the refrigeration instructions. Pour the Jell-O onto the cake, be careful. Make sure to pour slow, otherwise your pan will overflow with gelatin.
Put in the refrigerator for about 20-30 minutes to allow the Jell-O to sink in. The finishing touch is to put the entire tub of Cool Whip on top of the cake.