To prepare store-bought Jell-O, you will begin by boiling your water, then once it is boiling add your Jell-O packet to a mixing bowl and cover with water. Stir the mixture until it is completely dissolved. This typically takes around two minutes of stirring time. Once dissolved, add cold water, stir to combine, then pour into your desired mold. Refrigerate uncovered for anywhere from 2 to 6 hours.